For hanging pipe from a steel beam on 3/8 in threaded rod, the Eaton B-Line B3033-3/8PLN wide jaw C-clamp is the beam clamp to buy: Eaton lists a 500 lb load with a safety factor of 5, cULus listing, and a set screw and locknut in the box. Pick the B-Line B3034 when you want the higher 560 lb catalog rating on flanges up to 3/4 in, and the Fig. 66 when the flange is up to 1-1/4 in thick. Hang them on B-Line ATR 3/8 in all-thread rod, which Eaton lists at 730 lb.
None of these B-Line parts had an in-stock new Amazon listing on October 14, 2026, so buy them from an Eaton B-Line distributor or a plumbing or electrical supply house. To order on Amazon, see the nVent CADDY universal beam clamps below.
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This guide covers the whole hanger stack: clamp, rod, hex nuts, lock nuts, washers, and retaining straps. For what goes on the pipe at the bottom of the rod, see our pipe insulation guide for insulated lines and cast iron vs PVC for why heavy drain lines need closer support.
Quick comparison: beam clamps for 3/8 in rod
| Check | B3033 wide jaw | B3034 C-clamp | Fig. 66 C-type | B3036L malleable |
|---|---|---|---|---|
| Rod sizes | 3/8-16 to 3/4-10 | 3/8 to 3/4 in | 3/8 to 5/8 in | 3/8 to 3/4 in |
| Max flange | Not stated in catalog | 3/4 in | 1-1/4 in | Not stated in catalog |
| Load, 3/8 in rod | 500 lb | 560 lb | 610 lb | 300 lb |
| Listings | UL, cUL, FM; MSS SP-69/SP-58 Type 19 and 23 | UL, cUL; FM for 3/8 and 1/2 in | UL, cUL, NFPA 13; OSHPD seismic | UL, cUL; MSS Type 23 |
| Set screw torque, 3/8 in | 5 ft-lb | 5 ft-lb | 5 ft-lb | 5 ft-lb |
| Retaining strap | Buy separately | Buy separately | Fig. 69 strap fits | B3362 to B3365, order separately |
| Exact purchase | No in-stock new Amazon listing on Oct 14, 2026; buy from a B-Line distributor, or see the CADDY clamps below | No in-stock new Amazon listing on Oct 14, 2026; buy from a B-Line distributor, or see the CADDY clamps below | No in-stock new Amazon listing on Oct 14, 2026; buy from a B-Line distributor, or see the CADDY clamps below | Covered in text; buy the B3033 instead for most jobs |
All four are C-clamps that bite the bottom or top flange of a beam with a cupped set screw. The rod threads into the clamp body and a locknut sets it. The differences are jaw width, max flange thickness, and catalog load.
BEST OVERALL · 500 LB, SAFETY FACTOR 5
B-Line B3033-3/8PLN: wide jaw clamp for most pipe runs
Choose it when you are hanging copper, steel, or plastic pipe from the flange of a steel beam or bar joist and want one clamp to stock. Eaton lists the B3033-3/8PLN as malleable iron, cULus listed, rated 500 lb with a safety factor of 5, with the set screw and locknut included. The catalog adds FM approval and MSS SP-69/SP-58 Type 19 and 23.
The wide jaw is reversible, so it can hang from the top or bottom flange. Set the set screw to 5 ft-lb for 3/8 in rod, per the catalog. Eaton warns that over-torqued set screws damage clamps.
Skip it if the flange is thicker than the jaw opens. Measure the flange with a tape before you order; the catalog does not list a max flange for this model, so check the jaw against the beam on the first one.
Buy from an Eaton B-Line distributor or a plumbing or electrical supply house; we found no in-stock new Amazon listing on October 14, 2026.
HIGHEST RATING ON THIN FLANGES · 560 LB
B-Line B3034: C-clamp for flanges up to 3/4 in
Choose it when the flange is 3/4 in or thinner and you want the extra margin. The catalog lists 560 lb for 3/8 in rod, UL and cUL, and FM approval for 3/8 and 1/2 in rod. The locknut is included.
Skip it on wide-flange beams thicker than 3/4 in. Go to the Fig. 66 there.
Buy from an Eaton B-Line distributor or a plumbing or electrical supply house; we found no in-stock new Amazon listing on October 14, 2026.
BEST FOR THICK FLANGES · 1-1/4 IN THROAT
B-Line Fig. 66: reversible steel C-type for big beams
Choose it when the beam flange is up to 1-1/4 in thick. The catalog lists 610 lb with 3/8 in rod, UL and cUL listing, NFPA 13, and OSHPD seismic approval, with a locknut included. The Fig. 69 retaining strap fits it.
Skip it if every beam on the job is a light bar joist. The B3033 is simpler to stock and covers those.
Buy from an Eaton B-Line distributor or a plumbing or electrical supply house; we found no in-stock new Amazon listing on October 14, 2026.
The B3036L malleable C-clamp is the budget pick in the same family at 300 lb for 3/8 in rod. Use it for light single runs. For anything heavy, or in earthquake country, buy the higher-rated clamp and a strap.
THREADED ROD · 3/8-16, 10 FT
B-Line ATR 3/8X120 ZN: 3/8 in all-thread rod
Choose it when you need 3/8 in hanger rod for the clamp to carry. Eaton lists the ATR 3/8X120 ZN at 0.375 in diameter, 120 in long, steel, with a 730 lb load capacity. Cut it with a rod cutter or a hacksaw and spin a nut over the cut end first so it chases the threads clean.
Size the rod for the pipe, not just the clamp. The MSS SP-69 table in the next section calls for 3/8 in rod on steel pipe up to 2 in and copper up to 2 in; larger pipe goes to 1/2 in rod and up.
Skip it in wet, corrosive spaces like a pool equipment room or a crawlspace that floods. Ask for the stainless (SS4 or SS6) or hot-dip galvanized (HDG) version of the same rod there.
Buy from an Eaton B-Line distributor or a supply house; we found no in-stock new Amazon listing for the 3/8 in rod on October 14, 2026. Any 3/8-16 zinc-plated all-thread rod of the same finish as your nuts fills the same role, but check its load rating.
ON AMAZON · nVent CADDY UNIVERSAL BEAM CLAMPS, 3/8 IN ROD
nVent CADDY 3000037EG and 3100037PL: the in-stock Amazon alternatives
Choose it when you want to order the clamp on Amazon. None of the B-Line clamps or the B-Line rod above had an in-stock new Amazon listing on October 14, 2026. nVent CADDY makes a universal C-type beam clamp for 3/8 in rod in two throat sizes. nVent lists the 3000037 universal beam clamp for 3/8 in rod with a 3/4 in max flange; the 3000037EG on Amazon is the electrogalvanized finish. The 3100037PL is the thick-flange version for 3/8 in rod with a 1-1/4 in max flange.
nVent publishes the load rating, set screw torque and approvals for each part number on its product page and submittal sheet. Size your hangers from nVent’s rating for the exact part, not from the B-Line numbers in this guide. A rating belongs to one maker’s clamp and does not carry over to another, even when the two look alike.
Skip it if the job spec names B-Line or a specific listed clamp and strap. Buy the specified part from a supply house so the submittal matches what you install.
Rod size and hanger spacing by pipe size
Eaton’s pipe hanger catalog reprints the rod size and max spacing table from ANSI/MSS SP-69 and SP-58. Use it to pick rod size. For spacing, your plumbing code governs, and it is often tighter than MSS, especially for plastic pipe and PEX. Check your adopted code table before you lay out hangers.
| Pipe size | Steel pipe: rod | Steel pipe: max spacing | Copper tube: rod | Copper tube: max spacing |
|---|---|---|---|---|
| 1/2 to 3/4 in | 3/8 in | 7 ft | 3/8 in | 5 ft |
| 1 in | 3/8 in | 7 ft | 3/8 in | 6 ft |
| 1-1/4 in | 3/8 in | 7 ft | 3/8 in | 7 ft |
| 1-1/2 in | 3/8 in | 9 ft | 3/8 in | 8 ft |
| 2 in | 3/8 in | 10 ft | 3/8 in | 8 ft |
| 3 in | 1/2 in | 12 ft | 1/2 in | 10 ft |
| 4 in | 5/8 in | 14 ft | 1/2 in | 12 ft |
Add a hanger within a short distance of every change in direction, valve, and heavy fitting. A full 4 in cast iron line weighs far more than the same run in PVC, so do the math on the load per hanger before you trust any single clamp.
Hex nuts, lock nuts, and flat washers for threaded rod
The clamp and the rod get the attention, but the small parts decide whether the hanger stays at the height you set. For 3/8 in rod, every nut and washer must be 3/8-16 coarse thread (UNC). Fine-thread nuts will not go on.
- Hex nuts: buy plain 3/8-16 hex nuts in the same finish as the rod. Zinc on zinc-plated rod, stainless on stainless rod. Mixing stainless nuts on zinc rod in a wet space invites corrosion at the threads.
- Lock nuts: Eaton’s spec section says to “Use adjusting locknuts at upper attachments and hangers.” In trade use that means a second hex nut jammed against the first, or the locknut that ships with the beam clamp. Nylon-insert lock nuts hold well under vibration, like near a pump, but do not reuse them many times.
- Flat washers: use a 3/8 in flat washer under every nut that bears on strut, a trapeze bar, or a clevis hanger. USS pattern washers have a larger outside diameter than SAE pattern and spread the load better on strut.
- Rod couplings: if you join two rods, use a 3/8-16 coupling nut and thread each rod in to the center of the coupling.
Buy nuts and washers in boxes of 100. A single trapeze hanger with two rods uses at least eight nuts and four washers.
Retaining straps and seismic areas
A C-clamp holds by friction and set screw bite. A retaining strap wraps the far side of the flange so the clamp cannot walk off. Eaton’s catalog states that “NFPA 13 requires the use of retaining straps with all beam clamps installed in earthquake areas.” The catalog says the Fig. 69 strap is approved for use with any listed beam clamp, needs a 1 in minimum return, and is not UL Listed in lengths over 16 in.
Even outside seismic zones, it is good practice to strap clamps on lines near pumps, on vertical loads that could shift, and anywhere a clamp hangs from a sloped flange. A strap costs little next to a dropped pipe.
Do not drill, weld, or notch structural steel to hang pipe without the building engineer’s approval. Fire sprinkler piping is installed and inspected under NFPA 13 by licensed sprinkler contractors. Gas piping supports need a permit and inspection in most areas; call a licensed plumber or gas fitter for those.
How to install a beam clamp
- Measure flange thickness with a tape or caliper and confirm it fits the clamp’s max flange.
- Thread the rod into the clamp body before you set the clamp, then run the locknut up loose.
- Slide the clamp onto the flange with the set screw and rod positioned as the maker’s drawing shows. Keep the rod plumb under the clamp.
- Tighten the set screw to the catalog torque, 5 ft-lb for 3/8 in rod on these B-Line clamps. Where no torque is listed, Eaton says finger-tight plus 1/4 to 1/2 turn.
- Tighten the locknut against the clamp body.
- Add the retaining strap if required or if the clamp sees vibration.
- Hang the pipe, check slope with a level, and lock every lower nut with a jam nut.
Beam clamp FAQ
How much weight can a 3/8 beam clamp hold?
It depends on the clamp. In the Eaton B-Line catalog, the B3033 is rated 500 lb, the B3034 560 lb, the Fig. 66 610 lb, and the B3036L 300 lb with 3/8 in rod. Eaton lists the B3033 rating with a safety factor of 5.
What size threaded rod do I need for pipe hangers?
The MSS SP-69 table in the Eaton catalog calls for 3/8 in rod for steel pipe and copper tube up to 2 in, 1/2 in rod for 3 in pipe, and larger rod as pipe size goes up. Always check your local plumbing code for spacing.
Do beam clamps need retaining straps?
In earthquake areas, yes for sprinkler work: Eaton cites NFPA 13 as requiring retaining straps with all beam clamps there. Elsewhere a strap is good practice near pumps, on vibrating lines, and on sloped flanges.
How tight should a beam clamp set screw be?
Follow the clamp maker. Eaton lists 5 ft-lb for 3/8 in rod on the B3033, B3034, Fig. 66, and B3036L, and warns that over-torqued set screws damage clamps.
Should I use lock nuts or jam nuts on threaded rod?
Either works if it is tight. Eaton says to use adjusting locknuts at upper attachments and hangers. A second hex nut jammed against the first is the common trade method, and nylon-insert lock nuts help near vibrating equipment.
How we chose
This is a document-based comparison from a licensed plumber’s point of view. We chose clamps and rod from one maker so the catalog ratings use one method, then read Eaton’s B-Line pipe hanger catalog sections and product pages for each model. The two nVent CADDY clamps are listed because the B-Line parts had no in-stock Amazon listing; use nVent’s own rating for those parts. We did not test these parts. 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
- Eaton B-Line pipe hanger catalog, beam clamps section (PDF) (maker page: www.eaton.com/content/dam/eaton/products/support-systems/pipe-hangers/ph-20-catalog-sections/beam-clamps-section-pipe-hanger-catalog.pdf): ratings, max flange, listings, set screw torque, retaining strap notes.
- Eaton B3033-3/8PLN product page (maker page: www.eaton.com/us/en-us/skuPage.B3033-3%7B%7D8PLN.html): 500 lb, safety factor 5, cULus, set screw and locknut included.
- Eaton ATR 3/8X120 ZN product page (maker page: www.eaton.com/us/en-us/skuPage.ATR,%203%7B%7D8X120%20ZN.html): 3/8 in rod, 120 in length, 730 lb.
- nVent CADDY 3000037PL product page (nvent.com): universal beam clamp, 3/8 in rod, 3/4 in max flange.
- nVent CADDY 3100037PL product page (nvent.com): thick-flange universal beam clamp, 3/8 in rod, 1-1/4 in max flange.
- Eaton B-Line catalog intro and technical data (PDF) (maker page: www.eaton.com/content/dam/eaton/products/support-systems/pipe-hangers/ph-20-catalog-sections/intro-photos-tech-data-from-pipe-hanger-catalog.pdf): MSS SP-69 rod size and spacing table, locknut guidance.