Trailer D-Rings and Safety Chains: What Working Load Limit Means and How to Choose by Size and Grade

D-rings and safety chains are the hardware that holds things in place when something else lets go. A D-ring gives you a solid anchor point for tying down a load on the trailer deck. Safety chains are the backup connection between the trailer and the tow vehicle if the coupler or hitch ever comes apart. Both are sold by their ratings, and the most important number to understand is the working load limit.

This guide explains what working load limit (WLL) means and how it differs from break strength. Then it walks through choosing weld-on and bolt-on D-rings, choosing safety chain by size, grade, hook and length, and hooking safety chains up correctly. D-ring and chain specifications come from the RAM Trailer Products D-Rings and Safety Chain sheet (April 2024) unless another source is named. Ratings are quoted exactly as the catalog prints them.

Key takeaways

• Working load and break strength are two different numbers. RAM's bolt-on D-ring is printed as "6000# pull capacity/ultimate break strength, 2000# work load." The working load is the number to load against; the break strength is where the part fails.
• On RAM's D-rings, the working load is roughly one-third of the break strength. The 1 in. weld-on D-ring, for example, is printed at U.B.S. 46760 lbs and S.W.L. 15586 lbs. The ratio is not the same on every product or brand, so read the working load directly instead of dividing.
• Size and grade set a chain's rating. On the RAM sheet, 1/4 in. Grade 30 proof coil chain is rated 5200# cap., 1/4 in. Grade 43 is 7800# and 1/4 in. Grade 70 is 12600#.
• Each safety chain should cover the whole loaded trailer. The CURT catalog says each individual chain or cable must meet or exceed the trailer weight. The Buyers Products catalog says safety chains must have a holding capacity of at least the total weight of the trailer and contents.
• Cross the chains under the tongue. Both catalogs say to cross safety chains under the trailer tongue so the tongue will not drop to the road if it separates from the hitch, with enough slack to turn but not so much that the chains drag.

Terms used in this guide

• Working load limit (WLL): The load a part is rated to carry in use. The RAM sheet prints it as "work load" on its bolt-on D-rings and as "S.W.L." (safe working load) on its forged D-rings. The CURT catalog's tables for tie-down straps and transport binder chains call it "Work Load," and its binder chain listing says "Do not exceed work load limit."
• Break strength: The load at which the part breaks. The RAM sheet prints it as "ultimate break strength" or "U.B.S." (ultimate breaking strength). It is not a load you should plan to use.
• Capacity ("cap."): The single rating the RAM sheet prints for each safety chain assembly. The sheet does not say whether that number is a working load or a break strength, so see Step 3.
• D-ring: A D-shaped forged ring held by a mounting bracket. It gives a strap, chain or rope a fixed anchor point.
• Weld-on bracket: A bracket that is welded to the trailer frame or deck. RAM's weld-on D-rings are forged from C1045 steel.
• Bolt-on bracket: A bracket that bolts through the deck or frame, such as RAM's 2-hole bracket or its 4.5 in. x 5 in. bolt-on plate with square or round mounting holes.
• Grade: The chain grade printed on the assembly. RAM's safety chains are Grade 30, Grade 43 or Grade 70. In the RAM sheet, a higher grade gives a higher rating at the same chain size.
• S-hook with safety latch: The heat-treated S-hook RAM uses on its Grade 30 assemblies, with a latch that closes the hook opening.
• Forged slip hook: The forged hook RAM uses on its Grade 43 and Grade 70 assemblies. Some are listed with a safety latch and some without.
• Overall length: RAM states that all of its chain assemblies are measured at overall length, including the hook(s).

Step 1: Know which number is the working load limit

Most tie-down and towing hardware is printed with two ratings. The larger one is the break strength: the load at which the ring, chain or hook fails. The smaller one is the working load limit: the load the part is rated to carry in service. When you compare parts, compare working load to working load.

The RAM sheet shows both numbers on every D-ring, and the gap between them is large:

Table note: Figures are from the RAM Trailer Products D-Rings and Safety Chain sheet (April 2024). The ring sizes are the D-ring material diameter. The forged D-rings are listed as forged from C1045 steel.

On every RAM D-ring, the working load is about one-third of the break strength. That ratio is not universal. In the CURT catalog's transport binder chain table, for example, a 5/16 in. Grade 70 chain is listed at a 4,700 lbs. work load and an 18,800 lbs. break strength, about one-quarter. A rating that is only a break strength tells you less than you might think, so look for the working load before you buy.

Step 2: Choose a D-ring by mount and size

Start with how the D-ring will mount.

• Weld-on D-rings come with a bracket that is welded to the trailer. RAM's weld-on line runs from a 1/2 in. ring with a 2-1/2 in. x 2-3/8 in. inside (I.D.) up to a 1 in. ring with a 3 in. x 4 in. I.D.
• Bolt-on D-rings fasten through the deck or frame. RAM lists a 1/2 in. D-ring with a 2-hole mounting bracket, and a 3/8 in. ring on a 4.5 in. x 5 in. zinc bolt-on plate, in square-hole and round-hole versions.

Table note: RAM part numbers for reference: DR-120B, DR-120W, DR-580W, DR-340W and DR-1034W. Our listings for the 1/2 in. and 5/8 in. rings use the shorter numbers DR-12B, DR-12W and DR-58W.

To size a D-ring, add up what the tie-downs on that ring will carry and choose a ring whose working load covers it; CURT's catalog warns not to exceed the work load limit. Also match the ring I.D. to the hook or strap end you plan to use. A larger hook needs a ring with enough room inside. Browse more anchor points under D-Lashing Rings and Tie Downs.

Step 3: Choose safety chain by size, grade, hook and length

A safety chain assembly is a length of chain with a hook on one or both ends. On the RAM sheet, the rating climbs with chain size and with grade:

Table note: From the RAM Trailer Products D-Rings and Safety Chain sheet (April 2024). All RAM assemblies are zinc plated, and RAM states that lengths are overall, including the hook(s). The sheet prints the 3/8 in. x 35 in. Grade 43 assembly as "G43 high test" and the 3/8 in. x 41 in. assembly as "Grade 43 proof coil."

What "cap." means here. The RAM sheet prints one number per chain and does not label it a working load or a break strength. The CURT catalog lists the same figures for the same chain size and grade, such as 7,800 lbs. for 1/4 in. Grade 43, 11,700 lbs. for 5/16 in. Grade 43 and 16,200 lbs. for 3/8 in. Grade 43, in a column headed "Break Strength." Read a chain rating as the figure the catalog prints, and check the product listing for which kind of rating it is.

How strong does each chain need to be? The CURT catalog says each individual chain or cable must meet or exceed the trailer weight. The Buyers Products catalog says the safety chains must have a "holding" capacity of at least the total weight of the trailer and contents. Use the loaded weight of the trailer, not the empty weight.

Hook and length. Grade 30 assemblies on the RAM sheet use heat-treated S-hooks with a safety latch. Grade 43 and Grade 70 assemblies use a forged slip hook. Two-hook assemblies (the 3/16 in. x 48 in. chain and the 1/4 in. chains at 48 in., 54 in. and 60 in.) have a hook on each end. Choose an overall length that reaches the tow vehicle with the chains crossed and room to turn, without dragging.

From the RAM line we list a 1/4 in. x 36 in. one-hook safety chain, a 1/4 in. x 60 in. safety chain with two heat-treated S-hooks and a 3/8 in. x 41 in. Grade 43 safety chain with a forged slip hook. For a new trailer tongue, the safety chain kit includes two 1/4 in. x 36 in. S-hook chains with weld-on safety chain clips. See every option under Safety Chains.

Step 4: Hook up and inspect safety chains correctly

The right chain only helps if it is connected the right way. Here is what the catalogs and instructions in our library say:

• Cross the chains under the tongue. The CURT and Buyers Products catalogs both say to cross the safety chains under the trailer tongue so the tongue will not drop to the road or ground if it separates from the hitch.
• Set the slack. CURT says to leave enough slack so the vehicle can safely turn, and never to let the chains drag on the ground. Buyers Products says to set the chains to a length that allows for the vehicle's turning radius but will not drag in operation.
• Attach to the hitch, not the bumper. CURT says never to attach the safety chains to the bumper.
• Check them every time you hook up. RAM's coupler instructions list "Check that trailer safety chains are properly connected" as a before-towing step.
• Inspect for rust and wear. Lippert's trailer owner's manual lists inspecting safety chains for rust and wear as a pre-trip check, along with engaging the chains and the breakaway switch actuating chain securely.

The Buyers Products catalog also refers readers to SAE J684 for full safety chain specifications.

D-ring and safety chain ordering checklist

1. Loaded trailer weight: the trailer plus everything it will carry.
2. For each safety chain: a rating that meets or exceeds that loaded weight, by itself.
3. Chain size and grade: compare the printed ratings; a higher grade gives a higher rating at the same size on the RAM sheet.
4. Hook style: S-hook with safety latch, or forged slip hook.
5. Overall length (hooks included): enough to cross under the tongue and turn, without dragging.
6. How the chains attach to the trailer, such as weld-on safety chain clips.
7. For tie-down D-rings: the working load (S.W.L. or work load), not the break strength.
8. D-ring mount: weld-on bracket, or bolt-on bracket with the right hole pattern.
9. Ring I.D. large enough for the hooks or strap ends you will use.

Frequently asked questions

What does working load limit (WLL) mean?

It is the load a piece of hardware is rated to carry in use. RAM prints it as "work load" or "S.W.L." (safe working load). It is always lower than the break strength, which RAM prints as "ultimate break strength" or "U.B.S." CURT's transport binder chain listing says "Do not exceed work load limit."

Is break strength the same as capacity?

No. Break strength is where the part fails. On RAM's bolt-on D-ring, the 6000# figure is labeled "pull capacity/ultimate break strength," and the work load is 2000#. Always check which number a listing or catalog is quoting.

How do I convert a break strength to a working load?

Do not guess. On RAM's D-rings the working load is about one-third of the break strength, but CURT's Grade 70 transport binder chain is listed at about one-quarter. Use the working load the manufacturer prints.

How strong should my safety chains be?

The CURT catalog says each individual chain or cable must meet or exceed the trailer weight. The Buyers Products catalog says the chains must hold at least the total weight of the trailer and contents.

Why should safety chains be crossed?

CURT and Buyers Products both say to cross them under the tongue so it will not drop to the road if the trailer separates from the hitch.

What is the difference between Grade 30, Grade 43 and Grade 70 chain?

On the RAM sheet, the higher the grade, the higher the rating at the same chain size. A 1/4 in. chain is printed at 5200# cap. in Grade 30, 7800# in Grade 43 and 12600# in Grade 70. RAM's Grade 30 assemblies use S-hooks with a safety latch, and its Grade 43 and Grade 70 assemblies use a forged slip hook.

Does the chain length include the hook?

Yes, on RAM chain. RAM states that all of its chain assemblies are overall length, including the hook(s).

Weld-on or bolt-on D-rings?

Weld-on D-rings have a bracket welded to the trailer, and RAM offers them up to a 1 in. ring rated S.W.L. 15586 lbs. Bolt-on D-rings fasten through the deck or frame; RAM's 1/2 in. bolt-on D-ring is rated S.W.L. 4080 lbs, the same as its 1/2 in. weld-on ring.

What size D-ring do I need?

Choose a ring whose working load covers what the tie-downs on that ring will carry, and whose inside (I.D.) is big enough for your hooks. RAM's rings run from S.W.L. 4080 lbs (1/2 in.) to S.W.L. 15586 lbs (1 in.).

References

• RAM Trailer Products. D-Rings / Safety Chain catalog sheet, April 2024: D-rings and safety chains (work load, S.W.L., U.B.S., chain size, grade, hook type and overall length).
• RAM Trailer Products. Coupler installation instructions: before-towing checks, including that trailer safety chains are properly connected.
• CURT (Lippert). Trailer Parts and Accessories catalog: Proper Safety Chain Usage; safety chains with S-hooks and safety latch clevis hooks; transport binder safety chains; rings and tie-down anchors.
• Buyers Products. Product catalog: Proper Safety Chain Use.
• Lippert. Master Owner's Manual, Axles and Suspensions, Trailer Axle (2K-7K) Owner's Manual: pre-trip inspection of safety chains.
• Southwest Wheel product listings for RAM D-rings, RAM safety chains and safety chain kits (titles as listed).

Related guides

• How to Choose a Trailer Coupler: Ball Size, Tongue Type, Latch and Capacity
• Trailer Jack Types: A-Frame, Swivel, Drop-Leg and Square Tube, and How to Size One
• What Lights a Trailer Needs: Stop, Tail, Marker and License Lamps, and Sealed LED vs Incandescent

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