Get Kroil Clear (9.2). It has the highest flash point here and the fewest health warnings, so it suits tight cabinets. For brass stems with O-rings, take Silikroil.
All four are aerosol penetrants for seized threads, scored on the maker’s own safety data sheet and data sheet. Each was new and in stock on Amazon as of Oct 22, 2026, and each scores 7.0 or higher.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.
How the four compare on our spec score
Seven checks from each maker’s safety data sheet (SDS), data sheet and product page, equal weight. Every rule and input is in the method section near the end.
PlumbingPicks spec score out of 10, from the makers’ documents read Oct 22, 2026. It is not a customer rating or a test of how fast each one frees a bolt.
Nobody publishes a penetration test you can compare across brands, and we didn’t run one. So the score doesn’t claim one oil frees a nut faster. It scores what matters on a plumbing job and what each maker commits to in writing.
That means the flash point and aerosol class (you work near pilot lights and torches), the health hazards on the SDS (you spray inside cabinets), whether the maker says it’s safe on plastic and rubber (traps, washers and O-rings), VOC compliance, how long the maker says to let it soak, and whether the Amazon listing matches the maker’s part number.
The best-known can on the shelf, PB B’laster, scored 3.8 on the same checks. It’s in the left-out table with the reasons.
Each pick, in detail
What each maker publishes, which plumbing jobs each one suits and where each one lost points.
One health class on its SDS, and no Prop 65 warning
Kano names it for rubber seals and plastic parts
Odorless and non-staining
Cons
Still a flammable aerosol, Category 2
NSF H1 is a food-plant rating, not a drinking-water approval
Smaller can than Silikroil
10 oz aerosol174°F flashAerosol Cat. 2VOC under 1%NSF H1 169985
Buy it if
You’re freeing a nut inside a cabinet, a closet or a basement mechanical room where the smell and the vapors hang around, or you’re working near a water heater or a boiler.
Skip it if
You need a big can for a whole job of rusted steel unions. AeroKroil comes in more sizes, and Kano says it’s the same Kroil formula in every Original can.
Kroil Clear is the one I’d keep in the bag for inside work, and I’ve used it. Kano Laboratories, the maker of Kroil, sells it as its food-grade penetrant, and the 10 ounce aerosol is part CKS102. It scored 9.2.
The flash point is the main reason. Kano’s safety data sheet for the aerosol, dated August 31, 2025, prints 174°F. That’s higher than any other pick here and 42 degrees above AeroKroil’s 132°F. It scores 8.7 on that check.
It’s still a flammable aerosol, Category 2 on the SDS, like most cans in this test. The extra flash point margin is not a license to spray near a flame. It just gives you more room near warm pipe.
Its SDS lists one health class beyond fire and pressure: aspiration hazard, which means swallowing the liquid can get it into the lungs. The Kroil Original and Silikroil sheets add skin irritation, eye irritation and skin sensitization. That gave Kroil Clear an 8.5 on health, and it needs no California Prop 65 warning.
Kano’s product pages say Kroil Original may soften or swell certain plastics and rubber with long contact. For rubber seals and plastic parts, Kano names Kroil Clear or Silikroil as the ones to use. That’s a 10 on plastic and rubber, and it’s why I reach for it under a sink.
The rest are 10s. Kano’s data sheet says VOC under 1% and 50-state compliant. Kano’s FAQ says Kroil starts to penetrate in 15 to 30 minutes and does better with hours or overnight on heavy rust. The Amazon listing carries part CKS102 and the UPC on Kano’s sheet.
One thing to get straight: NSF H1 means it’s registered for incidental food contact in a food plant. It is not NSF/ANSI 61, the drinking-water standard. Keep it on the outside of the threads, not inside the pipe.
My call: this is the can for the occupied house. Odorless, the highest flash point here, and the maker says it’s the one for rubber and plastic.
Best for valve stems with rubber seals
Silikroil
(Kroil Penetrant with Silicone), 16.5 oz aerosol, part SK162
Silicone residue can get in the way of paint or sealant (my call)
16.5 oz aerosol132°F flashAerosol Cat. 250-state VOCMade in USA
Buy it if
You’re freeing a stuck shower valve stem, a gate valve, a hose bib stem or anything brass that turns against a rubber O-ring or packing, and you want it to keep turning.
Skip it if
You’ll solder, glue or seal the joint right after. Silicone left on the surface is the last thing you want under solder or a sealant.
Silikroil is Kroil with silicone added, and I’ve used it. Kano now calls it Kroil Penetrant with Silicone; the 16.5 ounce aerosol is part SK162. It scored 8.2.
Kano describes it for frozen bearings, slides, gate valves, hinges and chains. The silicone is the difference from Kroil Original. Kano says it adds longer lubrication and helps push moisture out, so the part you just freed keeps moving. That’s exactly what you want on a gate valve stem or a stiff hose bib.
It also has Kano’s backing for rubber. Kano’s FAQ says Kroil Original may soften or swell some plastics and rubber with long contact, and names Silikroil or Kroil Clear as the alternatives for rubber seals and plastic parts. That’s a 10 on the plastic and rubber check.
Where it lost points is the safety sheet. Kano’s SDS for the aerosol, dated November 6, 2025, prints a 132°F flash point, which scores 6.6. It lists four health classes: skin irritation, eye irritation, skin sensitization and aspiration hazard. That’s a 4.0 on health. Gloves and safety glasses are not optional with this one.
The aerosol class is the same Category 2 as Kroil Clear and AeroKroil, a 7. Kroil’s page says it’s 50-state VOC compliant, and it needs no Prop 65 warning.
Kano’s soak advice applies here too: 15 to 30 minutes to start, hours or overnight on heavy corrosion, then steady turning force rather than impact. The Amazon listing carries model SK162-1 and the UPC on Kano’s page, a 10.
My call: this is the can for brass stems that need to work again, not just come apart. Clean it off the threads before you put sealant or tape on them.
Best for rusted steel and galvanized
AeroKroil
(Kroil Original Penetrant), 10 oz aerosol, part KS102
Kano says it’s safe on steel, iron, brass and copper
Kano lists plumbing and piping among its uses
Same formula in the aerosol and the 8 oz drip can
Clear soak-time advice from the maker
Cons
132°F flash point
Four health classes on its SDS
Kano warns long contact can soften some plastics and rubber
10 oz aerosol132°F flashAerosol Cat. 2VOC under 1%Drip can: KL081
Buy it if
You’re fighting rusted steel: galvanized unions and nipples, closet bolts, old tub drain shoes, a stuck cast iron cleanout plug, rusted tank bolts.
Skip it if
The nut sits against a plastic trap or a rubber washer you plan to reuse. Take Kroil Clear or Silikroil there, as Kano itself suggests.
AeroKroil is the aerosol version of Kroil Original, the can people mean when they say Kroil, and I’ve used it. Kano’s data sheet lists the 10 ounce aerosol as part KS102. It scored 7.8.
Kano says it’s the exact same product in every Kroil Original can, liquid or aerosol. So the 8 ounce drip can, KL081, is the same oil when you’d rather drip it into a thread than spray a room. Kano’s data sheet lists plumbing and piping among its uses and says it’s safe on all metals.
Kano’s soak advice is the most detailed of any maker here. Its FAQ says Kroil starts to penetrate within 15 to 30 minutes. For heavy rust it says several hours or overnight, and in bad cases a second coat in the morning. Then use steady rotational force, not impact, until the part starts to move. That’s a 10 on soak directions.
It lost points on safety. Kano’s SDS for the aerosol, dated October 6, 2025, prints a 132°F flash point, a 6.6, and lists four health classes: skin irritation, eye irritation, skin sensitization and aspiration hazard, a 4.0.
On plastic and rubber, Kano is honest. It says Kroil is generally safe on most plastics but that long contact with certain plastics or rubber may cause softening or swelling. A published caution scores 7. On a galvanized union with no rubber anywhere near it, that caution doesn’t matter.
VOC is under 1% and 50-state compliant on Kano’s sheet, and it needs no Prop 65 warning, both 10s. The Amazon listing carries part KS102 and the UPC on Kano’s sheet, another 10.
My call: for old steel, this is the oil to put on the night before. Spray, wait, spray again, and turn it slowly in the morning.
Best for nuts beside plastic traps
WD-40 Specialist Penetrant
With Smart Straw, 11 oz aerosol, order number 300004
WD-40 says safe on most metals, plastics and rubbers as directed
Two health classes on its SDS, and no Prop 65 warning
Smart Straw sprays a pin stream or a wide fan
Low odor, 50-state VOC compliant
Cons
Extremely flammable aerosol, Category 1
Soak advice is only “several minutes”
Not the same product as blue-and-yellow WD-40 Multi-Use
11 oz aerosol147°F flashAerosol Cat. 1VOC 24.51%UPC 079567300007
Buy it if
You’re loosening a supply nut, a compression nut or a slip nut sitting right against a plastic trap, a plastic supply line or a rubber washer, and you want the maker to say that’s fine.
Skip it if
You’re anywhere near a lit pilot, a torch or a hot flue. Its aerosol is Category 1, the most flammable class here.
WD-40 Specialist Penetrant is a different product from the blue-and-yellow WD-40 Multi-Use can, and I’ve used it. WD-40’s data sheet lists the 11 ounce can as order number 300004. It scored 7.5.
Its strongest point for plumbing is the plastic and rubber statement. WD-40’s data sheet says it’s safe on most common surfaces, including most metals, plastics and rubbers, when used as directed, and to test a small area if unsure. It also lists pipe threads among its uses. That’s a 10.
Its safety sheet is shorter than Kroil Original’s on health. The SDS lists aspiration hazard and drowsiness or dizziness, two classes, a 7.0. WD-40 says it needs no Prop 65 warning and is 50-state VOC compliant, a 10. It’s also low odor, which you notice under a kitchen sink.
The fire check is where it falls. The flash point of the liquid is 147°F, a 7.4. But WD-40’s SDS classes the can as an extremely flammable aerosol, Category 1, the most flammable class here, and that scores 3. The propellant, not the oil, drives that rating. Its data sheet also lists it as an NFPA 30B Level 3 aerosol for storage.
Soak directions are thin. WD-40 says to saturate the surface and let it soak for several minutes, with no longer time for heavy rust. That’s a 5.
The Smart Straw is a real help in a cabinet. Flip it up for a pin stream into the thread, down for a wide spray. The Amazon listing carries part 300004 and the UPC on WD-40’s sheet, a 10. It showed only 3 left at Amazon on Oct 22, so the card may show no price at times.
My call: this is the can for slip nuts and compression nuts on plastic drain and supply parts. Keep it well away from the water heater’s burner.
The four side by side
Fire, health and material facts from each maker’s safety data sheet and data sheet.
From Kano Laboratories’ SDS and data sheets for Kroil Clear (Aug 2025), Silikroil (Nov 2025) and AeroKroil (Oct 2025), and WD-40 Company’s Specialist Penetrant SDS (Dec 2024) and data sheet (Aug 2026), read Oct 22, 2026. Health classes count GHS health hazards on the SDS beyond fire and pressure.
Penetrating oil, torches and pilot lights
Every can here is a flammable aerosol. The flash point and the aerosol class tell you how much margin you have.
Flash point of the liquid from each maker’s current SDS, read Oct 22, 2026. Higher is more margin near warm pipe. It is not a safe temperature for a flame.
Flash point is the lowest temperature at which the liquid gives off enough vapor to catch from a spark or flame. A copper line you just sweated, a flue pipe or a water heater jacket can be far hotter than any number on this chart.
The aerosol class is the other half. It rates the whole spray, propellant included. WD-40 Specialist Penetrant’s liquid flashes at 147°F, yet its SDS calls the can an extremely flammable aerosol, Category 1, because of how the spray burns.
Can
Aerosol class on the SDS
What the SDS says to do
Kroil Clear, Silikroil, AeroKroil
Flammable aerosol, Category 2
Keep away from heat, sparks and open flame; vapors can travel to an ignition source and flash back
WD-40 Specialist Penetrant
Extremely flammable aerosol, Category 1
Do not spray on an open flame or other ignition source; use only outdoors or in a well-ventilated area
Keep away from heat and ignition; Liquid Wrench adds extra caution in basements
My call on heat and oil: don’t mix them on the same joint at the same time. If a nut needs a torch, wipe the penetrant off, let the vapors clear, and then heat. On a gas water heater or boiler, turn the burner and pilot off before you spray anywhere near it.
Every one of these SDS sheets also says the vapor is heavier than air or to use good ventilation. In a basement or crawlspace, that means the vapor settles low, right where a water heater burner sits.
Which penetrating oils are safe on plastic and rubber
Plumbing nuts sit against plastic traps, rubber washers and O-rings. Here’s what each maker says in writing.
Can
What the maker says
Our check
Kroil Clear
Kano names it for rubber seals and plastic components
10
Silikroil
Kano names it for rubber seals and plastic components
10
WD-40 Specialist Penetrant
Safe on most metals, plastics and rubbers when used as directed; test a small area if unsure
10
AeroKroil
Generally safe on most plastics; long contact with certain plastics or rubber may cause softening or swelling
7
CRC Knock’er Loose (left out)
Data sheet says “Plastic safe: No”
5
PB B’laster, Liquid Wrench (left out)
No plastic or rubber statement in the documents we read
0
Where does this bite on a real job? A slip nut on a PVC or ABS trap, a plastic supply line’s coupling nut, the rubber cone washer on a toilet supply, the O-rings on a shower cartridge, and the rubber tank-to-bowl gasket under rusted tank bolts.
My call: on any of those, use one of the three cans with a clear maker statement, spray the metal thread rather than the plastic, wipe off what runs, and don’t leave it soaking overnight against rubber you plan to reuse. If the washer or O-ring is coming out anyway, it matters less.
Fumes, skin and eyes in a sink cabinet
You spray these with your head inside a cabinet. The SDS lists what each one can do to you.
Eye irritation; may damage fertility or the unborn child (Repr. 1B); aspiration hazard
Yes, naphthalene
Liquid Wrench L112 (left out)
Harmful if swallowed; skin irritation; eye irritation; drowsiness; aspiration hazard
Not stated
Aspiration hazard is on every sheet. It means that if the oil is swallowed, it can get into the lungs, which is why every maker says not to induce vomiting. Skin sensitization means repeat skin contact can set off an allergic rash later.
My call: nitrile gloves and safety glasses for any of these, and a fan blowing out of the cabinet. Use quick bursts aimed at the thread, not long blasts into the cabinet. Our nitrile gloves guide covers gloves that hold up to solvents.
Penetrating oil near drinking water lines
None of these is approved to touch drinking water. Here’s what the NSF codes on the cans actually mean.
Code you’ll see
What it means
Which can
NSF H1
Registered as a lubricant for incidental food contact in food plants
Kroil Clear (registration 169985)
NSF H2
Registered for food plants where there is no food contact
Kroil Original liquid in 8 oz and gallon (165745); CRC Knock’er Loose
NSF/ANSI 61
The standard for products that touch drinking water
None of the cans on this page
So an NSF H1 badge on Kroil Clear doesn’t make it a drinking-water product. It makes it the least bad choice when you can’t avoid spraying near a supply fitting.
My call: spray the outside of the nut and its threads, never into an open pipe or valve body. When the fitting is apart, wipe the threads clean before you put tape or dope on them, and run the water at the nearest faucet for a minute after the repair. For thread sealants that are listed for potable water, see our tape, dope and putty guide.
Which penetrating oil for which plumbing job
Pick the job. The matcher gives the can, the maker’s soak time and the one thing to watch.
Job
Use
Soak
Watch out
Slip nut on a plastic trap
WD-40 Specialist Penetrant
Spray the nut’s threads, wait several minutes, then turn by hand or with large pliers.
Wipe off what runs onto the plastic. Don’t leave it soaking overnight.
Supply line compression nut
WD-40 Specialist Penetrant
Several minutes, then a second spray if it doesn’t move.
Shut the stop valve first. Keep the spray outside the fitting, never into the line.
Shower valve stem or bonnet nut
Silikroil
15 to 30 minutes to start; hours or overnight if it’s heavily corroded.
Wipe the threads before the new cartridge goes in, and grease O-rings with the cartridge maker’s grease.
Stuck gate valve or hose bib stem
Silikroil
15 to 30 minutes on the packing nut and stem, then work it gently both ways.
Loosen the packing nut a little before you force the handle.
Galvanized union or cleanout plug
AeroKroil
Several hours or overnight, and a second coat before you put a wrench on it.
Steady force, not impact. If you’ll heat it later, wipe the oil off first.
Rusted closet bolts or toilet tank bolts
AeroKroil
15 to 30 minutes on light rust; overnight on heavy rust.
If the rubber tank gasket is staying, use WD-40 Specialist Penetrant instead. If the bolts spin, cutting them is often faster.
Near a water heater, boiler or torch
Kroil Clear
15 to 30 minutes to start; hours or overnight on heavy rust.
Turn the burner and pilot off first. All four cans are flammable; wipe the oil off and let vapors clear before any torch.
Picks follow each maker’s plastic, rubber and fire statements on this page. Soak times: Kano’s Kroil FAQ (15 to 30 minutes, hours or overnight for heavy rust) and WD-40’s data sheet (several minutes), read Oct 22, 2026. The other advice is my call.
How to use penetrating oil on a seized plumbing nut
The makers agree on the basics: get it on the joint, give it time, and come back with steady force.
1
Make it safe
Shut off the water to the fixture. Turn off any burner or pilot nearby, and get air moving out of the cabinet or room.
2
Clean the joint
Brush loose rust and scale off the threads so the oil can reach the gap. Kano says to apply it as close to the joint as possible.
3
Spray and wait
Wet the thread where nut meets pipe. Wait at least the maker’s time: several minutes for WD-40 Specialist, 15 to 30 minutes for Kroil.
4
Tap, then soak again
Liquid Wrench’s directions say to tap or vibrate the part and reapply until it comes free. On heavy rust, Kano says to leave it hours or overnight and recoat.
5
Turn it slowly
Use the right wrench and steady force. Kano says to avoid sudden impact until the fastener starts to move. Back it off a little, tighten a little, and work it out.
6
Clean up
Wipe the threads and the fixture. Bag the rags if you’ll use a torch nearby, and wash your hands.
Most broken parts come from giving up on the soak too soon and reaching for a bigger wrench. A shower valve bonnet that’s been in the wall twenty years has had twenty years to corrode. My call: on anything inside a wall, spray it, put the trim back loosely, and come back the next day.
Back up the pipe. On a shower valve, a sink supply or a hose bib, hold the valve body with a second wrench so the force goes into the nut, not the pipe behind the wall. Our monkey wrench vs pipe wrench guide covers which wrench fits which nut, and our shower valve socket set guide covers deep bonnet nuts.
Maker
What the directions say
How long
Kano (Kroil Clear, Silikroil, AeroKroil)
Apply close to the joint; repeat as needed; steady rotational force
15 to 30 minutes; hours or overnight on heavy rust
WD-40 Specialist Penetrant
Shake, saturate the surface, let soak
Several minutes
Liquid Wrench L112 (left out)
Spray liberally, allow to soak, tap, reapply until free
No time given
PB B’laster (left out)
No directions in the SDS we read
No time given in it
Popular penetrating oils we checked and left out
These are well-known cans and real products. Scored on the same seven checks, each came in under 7.0.
Can
Spec score
What we found
Why it’s out
Liquid Wrench L112
6.4
200°F flash point and 0% VOC; five health classes on its SDS; no plastic or rubber statement
Under 7.0 on health and materials
CRC Knock’er Loose 03020
4.8
Data sheet says “Plastic safe: No”; no soak directions; Amazon features say 11 wt oz where CRC says 13
Under 7.0 on four checks
PB B’laster 16-PB
3.8
SDS lists Repr. 1B (may damage fertility or the unborn child) and a Prop 65 naphthalene warning; no plastic or rubber statement
Reproductive hazard on its SDS
PB B’laster is the can on most truck shelves, and plenty of mechanics swear by it. On a plumbing page, though, it gave up the most where plumbing work needs it. Its SDS, revised June 9, 2022, lists a reproductive hazard and carries a California Prop 65 warning for naphthalene. Nothing we read from the maker says how it treats plastic or rubber.
Liquid Wrench L112 has the best fire numbers of any can here: a 200°F flash point and 0% VOC. Its SDS lists five health classes, though, and its data sheet only promises it’s safe on painted surfaces. CRC Knock’er Loose prints the most data of any maker, including a plain “No” on plastic safety, which is honest but rules it out under sinks.
How to choose in five questions
Question
If yes
If no
Is there plastic or rubber touching the nut?
Kroil Clear, Silikroil or WD-40 Specialist
Any of the four
Will the part need to keep turning, like a valve stem?
Silikroil
Next question
Is it rusted steel or galvanized?
AeroKroil, soaked overnight
Next question
Is there a burner, pilot or torch nearby?
Kroil Clear, with the burner off
Next question
Do you only want one can?
Kroil Clear
Match the job above
My call for a plumber’s bag: Kroil Clear for inside work and anything near rubber or heat, plus a can of AeroKroil for old steel. If you only carry one, carry Kroil Clear.
Penetrating oil frees threads; it doesn’t clean rust off a surface. For that job, see our rust remover guide. And for cutting new threads, use a real cutting oil from our pipe threading oil guide, not a penetrant.
Questions people ask
What is the best penetrating oil?
For plumbing work, Kroil Clear, 9.2 on our spec score. It has the highest flash point of our four picks, one health class on its SDS, and Kano names it for rubber seals and plastic parts.
What is the highest rated penetrating oil?
No maker publishes a test you can compare across brands. On our spec score, built from each maker’s safety and data sheets, Kroil Clear rates highest at 9.2, then Silikroil at 8.2.
Is Kroil better than WD-40?
They suit different jobs. AeroKroil has better soak directions and a lower aerosol fire class. WD-40 Specialist Penetrant has the clearer plastic and rubber statement and fewer health classes. Blue-and-yellow WD-40 Multi-Use is a different product.
What penetrating oil penetrates the deepest?
No maker publishes a depth test in a form you can compare, and we didn’t run one. Kano says Kroil works by capillary action and starts to penetrate in 15 to 30 minutes.
Why does Kroil work so well?
Kano says Kroil’s low surface tension lets it creep into very tight gaps by capillary action. Its directions also call for long soaks, hours or overnight on heavy rust, which is what frees most seized threads.
Is penetrating oil safe on plastic pipe?
Depends on the can. WD-40 says its Specialist Penetrant is safe on most plastics and rubbers as directed. Kano names Kroil Clear and Silikroil for plastic parts. CRC’s data sheet says Knock’er Loose is not plastic safe.
Can I use penetrating oil on a shower valve?
Yes, on the bonnet nut and stem threads. Silikroil suits brass stems with rubber O-rings. Shut the water off, soak 15 to 30 minutes or longer, and wipe the threads before the new cartridge goes in.
Is penetrating oil flammable?
Yes. All seven cans we checked are flammable aerosols on their SDS. WD-40 Specialist Penetrant is Category 1, extremely flammable. Turn off nearby burners and pilots, and never spray toward a flame.
Can you use penetrating oil and then a torch?
Not at the same time. Every SDS here says to keep the oil away from heat and flame. My call: wipe the oil off, let the vapors clear, then heat.
Is penetrating oil safe for drinking water lines?
None of these is approved for drinking water. NSF H1 on Kroil Clear is a food-plant rating, not NSF/ANSI 61. Spray only the outside of the nut, and flush the line after.
How long should penetrating oil soak?
Kano says Kroil starts working in 15 to 30 minutes and does best with hours or overnight on heavy rust. WD-40 says several minutes for its Specialist Penetrant.
Is PB Blaster good for plumbing?
It’s a well-known penetrant, but it scored 3.8 here. Its SDS lists a reproductive hazard and a Prop 65 naphthalene warning, and its maker’s documents we read say nothing about plastic or rubber.
How we picked these
Why trust me
I’m Isaac Daniels, a licensed journeyman plumber in Georgia (license #JP507711), and I’ve used all four picks. Every fact here comes from Kano Laboratories’, WD-40 Company’s, B’laster’s and CRC’s own safety data sheets, data sheets and product pages, read Oct 22, 2026. Where I add advice of my own, it’s labeled as my call.
How I pick
Only aerosol penetrating oils for seized threads, from documented makers, new and in stock on Amazon, checked through Amazon’s product data the same day.
The listing’s part number has to match the maker’s documents.
Each card’s spec score comes from the seven checks below. All four score 7.0 or higher; three popular cans scored under and are listed with the reasons.
The spec score, check by check
All seven checks carry the same weight, and each runs from 0 to 10. Where two sheets from one maker disagree, as CRC’s did on flammability, the less favorable figure counts. The score reads paperwork from Kano, WD-40, Blaster, CRC and Liquid Wrench; it is not a spray test, and buyers’ opinions play no part in it.
Check (weight)
How it’s scored
Flash point (1/7)
10 × flash point °F ÷ 200, capped at 10, from the SDS
Aerosol class (1/7)
10 for Category 3 or not flammable; 7 for Category 2; 3 for Category 1
Health hazards (1/7)
10 minus 1.5 for each GHS health class on the SDS (beyond fire and pressure); minus 3 more for a reproductive or cancer class or a Prop 65 warning; not below 0
Plastic and rubber (1/7)
10 when the maker says it’s safe on plastic and rubber or names it for rubber seals; 7 for a published caution; 5 when the maker says it isn’t plastic safe; 0 for nothing published
VOC (1/7)
10 when the maker states 50-state VOC compliance; 5 for a published VOC % only; 0 for neither in the documents read
Soak directions (1/7)
10 when the maker gives a soak time range; 5 for “let it soak” with no time; 0 for none
Listing match (1/7)
10 when the Amazon listing’s part number and size match the maker; 5 for one conflict; 0 if it can’t be tied to a model
Total
Average of the checks, to one decimal
Can
Flash
Class
Health
Plastic
VOC
Soak
Listing
Score
Kroil Clear
8.7 (174°F)
7
8.5 (1)
10
10
10
10
9.2
Silikroil
6.6 (132°F)
7
4.0 (4)
10
10
10
10
8.2
AeroKroil
6.6 (132°F)
7
4.0 (4)
7
10
10
10
7.8
WD-40 Specialist
7.4 (147°F)
3 (Cat. 1)
7.0 (2)
10
10
5
10
7.5
Liquid Wrench L112
10 (200°F)
7
2.5 (5)
0
10
5
10
6.4
CRC Knock’er Loose
7.4 (147°F)
7
4.0 (4)
5
5
0
5
4.8
PB B’laster 16-PB
7.1 (over 141°F)
7
2.5 (3 + Repr.)
0
0
0
10
3.8
PB B’laster’s soak and VOC scores are 0 because the maker documents we could read, its SDS, give neither a soak time nor a VOC statement. Its data sheet wouldn’t load for us on Oct 22, so if it states them, PB would gain points, though not enough to reach 7.0.
Sources
Kano Laboratories, Kroil Clear Aerosol SDS (Aug 31, 2025) and Kroil Clear Food Grade Penetrant data sheet: read Oct 22, 2026.
Kano Laboratories, Kroil Penetrant with Silicone Aerosol SDS (Nov 6, 2025) and Silikroil product page and FAQ (kroil.com): read Oct 22, 2026.
Kano Laboratories, Kroil Penetrant Original Aerosol SDS, formerly AeroKroil (Oct 6, 2025), Kroil Original data sheet and product page and FAQ (kroil.com): read Oct 22, 2026.
WD-40 Company, WD-40 Specialist Penetrant SDS (Dec 18, 2024), technical data sheet (08/2026) and product page (wd40.com): read Oct 22, 2026.
Blumenthal Brands Integrated, Liquid Wrench Penetrating Oil L112 SDS version 17 (Nov 7, 2022) and product information sheet (liquidwrench.com): read Oct 22, 2026.
CRC Industries, Knock’er Loose 03020 SDS and data sheet (crcindustries.com): read Oct 22, 2026.
Blaster LLC, PB Penetrating Catalyst aerosol SDS version 2.0 (June 9, 2022) (blasterproducts.com): read Oct 22, 2026. Its 16-PB data sheet would not load that day.
U.S. Consumer Product Safety Commission recall search for these brands: no penetrating oil recalls found, Oct 22, 2026. Health Canada recalled a Liquid Wrench liquid bottle in 2023 for packaging; it is not a pick here.
Brand-written Amazon listing text and item data for B0DH44S1MV, B0036RNKCO, B000F09CEA, B00631GQGW and the left-out cans: read through Amazon’s product data, Oct 22, 2026.
Google results for “best penetrating oil”: seen Oct 22, 2026. Search volume from Semrush, Oct 22, 2026.
