For wall-hung sink brackets and other plumbing hardware that bolts into wood blocking, buy Hillman galvanized hex lag screws sized to the bracket hole (the 3/8 in x 2-1/2 in pack fits most heavy brackets) and drill a proper pilot hole. If you would rather skip the pilot hole, the Simpson Strong-Tie SDWS22300DB timber screw is the maker’s load-rated lag alternative. In wet spots use Hillman stainless #8 x 1-1/2 in wood screws, and keep a Hillman 130280 wood screw assortment in the truck for everything else.
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A wall-hung fixture is only as strong as the wood behind it. Our wall-mounted toilet guide covers floor-mounted carriers, and our farmhouse sink guide covers the heavy sinks that need cabinet or frame support. This page is about the screws and bolts themselves.
Quick picks: lag screws and screws for plumbing work
| Check | Hillman galvanized lag | Simpson SDWS22300DB | Hillman stainless wood screws | Hillman wood screw kit |
|---|---|---|---|---|
| Size | 3/8 in x 2-1/2 in hex lag, hot-dip galvanized; linked listing is Hillman 812065, 50 pc | SDWS Timber, 0.220 in x 3 in, exterior grade; linked listing is the 50-count SDWS22300DB-R50 | #8 x 1-1/2 in Phillips flat head, 25 pc | Assorted sizes; linked kit is Hillman 130280 (360 pc, zinc, brass and black phosphate) |
| Pilot hole | Yes, shank and thread lead holes | Simpson typically does not require predrilling | Yes in hardwood; helps in all wood | Yes in hardwood |
| Corrosion | Galvanized | Double-barrier coating | Stainless | Zinc, brass and black phosphate finishes: dry, indoor use |
| Choose it for | Wall-hung sink brackets, carrier and ledger bolting into blocking | Same jobs, faster, no pilot hole | Vanity backs, access panels, anything in a wet area | Pipe straps, brackets, cabinet work, general repairs |
| Exact purchase | Check Hillman 3/8 x 2-1/2 galvanized lag on Amazon → | Check Simpson SDWS22300DB-R50 on Amazon → | Buy from a Hillman dealer; no in-stock new Amazon listing on Oct 14, 2026 | Check Hillman 130280 wood screw kit on Amazon → |
BEST LAG SCREW FOR SINK BRACKETS · GALVANIZED
Hillman galvanized hex lag screws, 3/8 in x 2-1/2 in
Choose it when you are fastening a wall-hung lavatory bracket, a heavy pipe support, or a strut channel to 2x wood blocking. Match the lag diameter to the hole in the bracket, then pick a length that goes through the drywall and most of the way through the blocking. With 1/2 in drywall over 1-1/2 in blocking laid flat, 2-1/2 in is about right. The Amazon listing we link is Hillman 812065, hot-dipped galvanized, 3/8 in x 2-1/2 in, 50-pack.
Drive lags with a wrench or impact on low, never a hammer. The USDA Forest Products Laboratory’s Wood Handbook says lag screws “should always be inserted by turning with a wrench, not by driving with a hammer,” and that soap or a similar lubricant helps them turn.
Skip it if the bracket hole is smaller than 3/8 in. Buy the size that fills the hole: 1/4 in and 5/16 in lags are common on lighter sink hangers. Also skip zinc or plain lags in pressure-treated wood.
BEST NO-PILOT LAG ALTERNATIVE · LOAD-RATED
Simpson Strong-Tie SDWS22300DB: timber screw in place of a lag
Choose it when you have a lot of blocking or ledger to fasten and want to skip the two-step pilot hole. Simpson’s engineering blog calls its screws “a great load-rated alternative to lag screws because they require no predrilling,” and says most of its screws come in a double-barrier coating or Type 316 stainless. Simpson publishes an engineering letter (L-F-LAGSUB23) that lists which of its screws meet or exceed lag screw shear values. The Amazon listing we link is SDWS22300DB-R50, a 50-count pack of the same 0.220 in x 3 in screw.
Drive it with the bit in the box and a drill or impact driver. A right-angle drill helps in a tight stud bay.
Skip it when a fixture maker’s instructions call for a specific lag size. Follow the fixture instructions; swap only with the engineering letter in hand.
BEST STAINLESS STEEL SCREWS · WET AREAS
Hillman stainless Phillips flat wood screws, #8 x 1-1/2 in
Choose it when the screw lives where water does: under a sink, behind an access panel at a tub, in a laundry box, or on an outdoor hose bib bracket. Zinc screws rust and stain in those spots. Stainless costs more and is a little softer, so use a good-fitting bit and do not overdrive.
For an outdoor bracket into treated wood, step up to Hillman stainless hex lag screws (sold in sizes like 1/2 in x 3-1/2 in) rather than zinc.
Skip it for structural or heavy loads. A #8 screw is for panels and light brackets, not a sink.
Buy from a Hillman dealer or hardware store; we found no in-stock new Amazon listing for this exact screw on October 14, 2026.
BEST WOOD SCREWS ASSORTMENT · TRUCK STOCK
Hillman 130280 wood screw assortment kit
Choose it when you want one box that covers pipe straps, valve box brackets, cabinet backs, and small repairs. An assortment saves a trip when the screw that came with a part is too short.
The Amazon listing we link is Hillman 130280, a large assorted wood screw kit of 360 pieces in zinc, brass and black phosphate finishes. Hillman’s zinc-only wood screw kit had no in-stock new Amazon listing on October 14, 2026.
Skip it for anything wet or outdoors. These finishes are for dry indoor spots. Keep a separate box of stainless screws.
Pilot hole sizes for lag screws
Most stripped or split lag jobs come down to the pilot hole. The Wood Handbook gives a two-part rule: the lead hole for the smooth shank should be the same diameter as the shank, and the lead hole for the threads should be a percentage of the shank diameter based on the wood.
| Wood | Thread lead hole, % of shank diameter | Example: 3/8 in lag | Notes |
|---|---|---|---|
| Low-density softwoods (cedars, white pines) | 40% to 70% | About 5/32 to 1/4 in | Use the low end for small lags |
| Douglas-fir and Southern Pine | 60% to 75% | About 7/32 to 9/32 in | Most framing lumber and blocking |
| Dense hardwoods (oaks) | 65% to 85% | About 1/4 to 5/16 in | Use the high end for large lags |
The handbook says the smaller percentage in each range applies to smaller-diameter lags and the larger to larger lags. The example column is that math rounded to common bit sizes. Drill the shank hole first, as deep as the smooth shank, then the smaller thread hole the rest of the way.
- Hold the bracket level on the wall and mark the holes through it.
- Confirm blocking behind each mark with a small test hole. If you hit air, stop. You need blocking.
- Drill the shank-size hole through the drywall and as deep into the wood as the shank is long.
- Drill the thread lead hole to full depth.
- Rub a little bar soap on the threads, add a flat washer, and turn the lag in with a socket until the bracket is snug. Do not keep cranking once it seats.
Machine screws and hex bolts: what to buy
Machine screws thread into a nut or a tapped hole, not into wood. In plumbing they hold overflow plates, shower drain covers, faucet handles and escutcheons, and toilet seat hinges. Buy them by thread size and length, in stainless for anything near water. A small stainless assortment with nuts covers most fixture trim. Take the old screw to match the thread before you buy, because two sizes can look alike and not fit.
Hex bolts (hex cap screws) bolt through two parts with a nut. For plumbing work, 3/8-16 hex bolts with nuts and flat washers are the common size for joining strut channel and trapeze hangers, and they match 3/8 in hanger rod. Buy zinc for dry indoor work and hot-dip galvanized or stainless for damp spaces. Grade 5 bolts are stronger than plain Grade 2 hardware-store bolts; use what the strut or hanger maker calls for.
Hanging pipe from steel instead of wood? That job takes a beam clamp and 3/8 in hanger rod, with nuts and washers in one matching finish.
Where plumbers use lag screws and when to call a pro
- Wall-hung sinks: the hanger bracket is lagged into blocking at the height the sink maker lists. The sink should not rely on the drain or supply for support.
- Fixture carriers: floor-mounted carriers bolt to the floor and carry wall-hung toilets and some lavatories. Lags into wood are not a substitute for a carrier the fixture maker requires.
- Water heater platforms and straps: straps and stands fasten into studs or solid framing with the screws the kit specifies.
- Pipe supports: strut and straps fastened to joists or blocking.
If the wall has no blocking and the fixture is heavy, open the wall and add it. If the framing is damaged, rotted, or steel stud, or the fixture is commercial or ADA, call a licensed plumber. Some jurisdictions require a permit to replace a fixture or alter its support.
Lag screw FAQ
What size pilot hole do I need for a lag screw?
Drill the shank part the same diameter as the shank. For the threaded part, the USDA Wood Handbook gives 60% to 75% of the shank diameter for Douglas-fir and Southern Pine, 40% to 70% for low-density softwoods like cedar, and 65% to 85% for dense hardwoods like oak.
Can I use a hammer to start a lag screw?
No. The USDA Wood Handbook says lag screws should always be turned in with a wrench, not driven with a hammer. A little soap on the threads makes turning easier.
What screws should I use to hang a wall-hung sink?
Use the lag size the sink or bracket maker lists, into solid wood blocking or a carrier. Fill the bracket hole with the largest lag it accepts, and pick a length that reaches well into the blocking.
Are structural screws as good as lag screws?
Simpson Strong-Tie says its screws are a load-rated alternative to lag screws and do not require predrilling, and it publishes an engineering letter listing which screws meet or exceed lag screw shear values. Follow the fixture maker if it names a specific lag.
Should I use stainless steel screws in a bathroom?
Yes for anything that stays wet or damp, like access panels, under-sink brackets, and outdoor hose bib mounts. Zinc screws rust and stain in those spots. Indoors and dry, zinc is fine.
How we chose
This is a document-based guide from a licensed plumber’s point of view. We chose common, stocked fasteners for the lag, wood, stainless, machine screw and hex bolt jobs plumbers do most, then checked install guidance against the USDA Forest Products Laboratory Wood Handbook and Simpson Strong-Tie’s engineering notes. We did not test these fasteners. Sources were read October 14, 2026; sellers and availability change. We do not publish prices. More about our selection method and Plumbing Picks.
Primary sources
- USDA FPL Wood Handbook, chapter 8: Fastenings (PDF) (source: www.fpl.fs.usda.gov/documnts/fplgtr/fplgtr282/chapter_08_fpl_gtr282.pdf): lag and wood screw lead holes, turning not hammering, lubricant.
- Simpson Strong-Tie engineering blog: fastener inquiries (seblog.strongtie.com): screws as a lag alternative, no predrilling, L-F-LAGSUB23, coatings.
- Simpson Strong-Tie SDWS Timber screw product page (strongtie.com): model family.
- Hillman galvanized hex lag screws 3/8 in x 2-1/2 in (shop.hillmangroup.com): size and pack.
- Hillman stainless Phillips flat wood screws #8 x 1-1/2 in (shop.hillmangroup.com): size and pack.
- Hillman zinc wood screw assortment kit (shop.hillmangroup.com): Hillman’s zinc-only kit, which had no in-stock new Amazon listing on October 14, 2026.
- Hillman stainless steel hex lag screws 1/2 in x 3-1/2 in (shop.hillmangroup.com): outdoor stainless lag size.