Transport Restraints and Tie-Downs for Hardware Moves
Tie-downs are the straps, chains, binders and anchor hardware that hold cargo to a vehicle. On US roads FMCSA's 49 CFR 393 Subpart I governs them: the tiedowns on an article must add up to a working load limit of at least half its weight, and the count depends on the article's length.
Updated
Restraint types and where they are used
Restraint is a system: the transport fixture or crate, the tiedowns, the tensioners, the anchor points on the vehicle and anything that blocks or braces the load. 49 CFR 393.108(a) makes the point directly: a tiedown's working load limit is the lowest of any of its components, including the tensioner, or of the anchor points it attaches to.
| Item | What it does | Default WLL if unmarked, 49 CFR 393.108 tables |
|---|---|---|
| Synthetic web strap with ratchet | Most common tiedown for crates, fixtures and GSE | 2 in webbing: 2,000 lb; 3 in: 3,000 lb; 4 in: 4,000 lb |
| Transport chain (grade 70) with binder | Heavy fixtures, steel GSE, machinery | 3/8 in: 6,600 lb |
| Alloy chain (grade 80 or 100) | Heavy loads where alloy chain is preferred | 3/8 in: 7,100 lb (grade 80), 8,800 lb (grade 100) |
| Wire rope | Heavy or long items | 3/8 in 6x37 fiber core: 3,000 lb |
| Friction mat | Adds resistance to sliding | Unrated mats count as 50 percent of the weight on the mat |
| Blocking, bracing, dunnage, chocks | Stop sliding and rolling without relying on tiedowns alone | Must be free of damage or defects (393.104(d)) |
| Edge protection | Keeps straps from being cut at corners | Required where a tiedown would be abraded or cut (393.104(f)(4)) |
Shock and tilt indicators and data loggers do not restrain anything; they record what happened. They are covered in crating and packaging.
The rules that govern cargo securement
49 CFR 393 Subpart I applies to trucks, truck tractors, semitrailers, full trailers and pole trailers on public roads. The sections a shipper of flight hardware actually uses are below.
| Section | What it requires |
|---|---|
| 393.102 | Securement must withstand, without exceeding breaking strength, 0.8 g deceleration forward, 0.5 g rearward and 0.5 g lateral; and without exceeding working load limit, 0.435 g forward, 0.5 g rearward and 0.25 g lateral. Articles not fully inside the vehicle structure need a downward force of at least 20 percent of their weight |
| 393.104 | No damaged or weakened components; no knots; repairs to the applicable standard or maker's instructions; edge protection where needed; tiedown assemblies built to listed standards |
| 393.106 | Aggregate working load limit at least one half the article's weight; rolling articles chocked, wedged or cradled |
| 393.108 | How to determine working load limit from markings or the default tables |
| 393.110 | Minimum number of tiedowns by article length and weight |
| 393.112 | Tiedowns must be adjustable so the driver can tighten them in transit (steel strapping excepted) |
393.104(e) names the standards tiedown components must conform to: WSTDA-T1 (1998) for synthetic webbing, the National Association of Chain Manufacturers' Welded Steel Chain Specifications (September 2005) for chain, the Wire Rope Technical Board's Wire Rope Users Manual (2nd edition, 1985) for wire rope, ASTM D3953-97 for steel strapping, and Cordage Institute specifications for fiber rope.
Have a part like this?Send it in under a minute. A person replies within 1 business day.Reading chain and strap markings
Working load limit comes from the maker's marking, and only falls back to the regulation's tables when there is no marking. Chain grade is marked on the links, and the tables in 393.108 show three accepted forms of the mark.
| Chain grade | Mark form 1 | Mark form 2 | Mark form 3 |
|---|---|---|---|
| Grade 30 proof coil | 3 | 30 | 300 |
| Grade 43 high test | 4 | 43 | 430 |
| Grade 70 transport | 7 | 70 | 700 |
| Grade 80 alloy | 8 | 80 | 800 |
| Grade 100 alloy | 10 | 100 | 1000 |
- Welded chain with no grade or WLL marking is treated as grade 30 proof coil, the lowest in the table (393.108(d)).
- Wire rope with no WLL marking gets one fourth of the nominal strength in the Wire Rope Users Manual; rope of unknown construction is treated as 6x37 fiber core (393.108(e)).
- Synthetic cordage that cannot be identified is treated as polypropylene (393.108(c)).
- A tiedown marked with a WLL different from the table is taken at its marked value (393.108(b)).
So the label on a ratchet strap is not decoration. An unlabeled 2 in strap counts as 2,000 lb no matter what the seller claimed.
Working out the tiedowns for a load
Do two checks: the count by length, and the aggregate working load limit against weight. 393.110 sets the count when the article is not blocked against forward movement by a headerboard, bulkhead or other blocking.
- 5 ft or shorter and 1,100 lb or lighter: at least one tiedown.
- 5 ft or shorter and over 1,100 lb, or over 5 ft up to 10 ft at any weight: at least two.
- Over 10 ft: two, plus one more for every 10 ft or fraction beyond the first 10 ft.
- If the article is blocked forward: at least one tiedown per 10 ft of length or fraction.
For the aggregate, 393.106(d) counts one half the WLL of a tiedown that runs from the vehicle to an anchor point on the article, or that passes over or around the article and returns to the same side, and the full WLL of one that passes over or around the article to the other side of the vehicle.
A worked example: a crated assembly 8 ft long weighing 4,000 lb, not blocked forward, needs at least two tiedowns and an aggregate WLL of at least 2,000 lb. Two 2 in straps with a 2,000 lb WLL thrown over the crate side to side give 4,000 lb aggregate. Four 3/8 in grade 70 chains attached directly to the crate's tiedown points count half their 6,600 lb WLL each, 13,200 lb aggregate. Both meet the rule. The regulation is a floor; flight hardware usually needs more, because its own acceleration limits are often lower than what securement rules assume. The shipping flight hardware guide covers air ride and dedicated trucks.
393.110(d) exempts vehicles carrying machinery or fabricated structural items that must be fastened by special methods from the count rule, but those articles must still be securely and adequately fastened.
Ratchets, binders and anchor points
- Tensioners count. Under 393.108(a) a ratchet or binder with a lower WLL than the strap or chain sets the tiedown's WLL. Buy matched assemblies with the WLL on the label or tag.
- Adjustable in transit. 393.112 requires that the driver can tighten each tiedown in transit, which rules out tiedowns that cannot be re-tensioned (steel strapping is the stated exception).
- Anchor points. 393.104(c) requires vehicle anchor points, floors, walls and stake pockets to be strong enough for the performance criteria, with no cracks or damage. The anchor's own rating can be the limit.
- Knots and repairs. 393.104(f) bans knots in tiedowns and requires repairs to follow the applicable standard or the maker's instructions.
- Edges. Use edge protection that resists abrasion, cutting and crushing wherever a strap touches a crate corner or fixture edge.
Transport fixtures and air shipment
The tiedowns are only as good as the points they attach to on the fixture. A transport fixture, cradle or dolly should have dedicated tiedown points designed for the securement loads, marked with their rating, and shown on the drawing. Do not tie down through a lifting point or a caster mount unless the analysis covers that load direction; lifting and restraint loads go in different directions. See lifting points and hoist rings and casters and wheels.
Air shipment has its own restraint rules set by the aircraft operator or air carrier, and military airlift programs publish their own. Ask the carrier for its restraint requirements and tiedown limits before the fixture is designed, not at the ramp. Pressurized items, batteries and some chemicals bring hazardous materials rules, and exports bring EEI filing; both are covered in shipping flight hardware.
Ordering checklist
- Type, width or size, length, end fittings (hooks, D-rings, chain grab hooks) and tensioner type for each tiedown.
- Marked working load limit on each assembly, with the tensioner and fittings rated at least as high.
- Standard conformance per 49 CFR 393.104(e): WSTDA-T1 for webbing, NACM specifications for chain.
- Chain grade and marking form; no unmarked chain.
- Edge protectors, friction mats with a rated value, chocks and blocking material.
- Shock, tilt and temperature indicators or a data logger for sensitive hardware.
- Transport fixture tiedown point ratings and locations on the drawing.
- Certificate of conformance; see certificate of conformance.
Quality risks and how to receive tie-downs
The usual problem is an overstated or missing rating. A strap without a legible WLL label falls back to the regulation's table value, and unmarked chain counts as grade 30. Cheap ratchets can carry a lower rating than the webbing they come with, which lowers the whole assembly under 393.108(a).
- At receiving, confirm the WLL label is present, legible and matches the PO for every assembly, and that chain carries a grade mark.
- Inspect webbing for cuts and stitching damage, and hooks and binders for cracks or distortion; 393.104(b) bars damaged or weakened components.
- Keep tiedowns with the transport fixture or crate they were sized for, and replace damaged ones rather than knotting or field repairing them.
See receiving inspection.
How we source transport restraints
We do not stock tie-downs, publish prices or claim authorized distributor status for any maker. We source rated assemblies through makers and their authorized channels, flow down the marking and standard requirements, and put them on one purchase order with the transport fixture, crate or GSE they secure, so the restraint arrives sized for the load it carries. Related: slings and rigging hardware, the GSE components category, the parts index and our ground support equipment service.
Get tie-downs and transport fixtures quoted
Send the article weight, dimensions, center of gravity, how it will travel and any acceleration limits, and we will return sourced restraints, fixtures and crating with a lead time. A person replies within one business day. Request a quote for transport restraints.
Send the job. A person replies within 1 business day.
Part, quantity and date are enough to start. Drawings and the mutual NDA follow by reply, and controlled programs never send technical data through this site.
We have it.
Reference . A person replies within 1 business day. Watch for our email from [email protected].
Questions
How many tie-downs do I need for a crate on a truck?
Under 49 CFR 393.110, if the crate is not blocked against forward movement: one tiedown if it is 5 ft or shorter and 1,100 lb or lighter; two if it is 5 ft or shorter and heavier, or between 5 and 10 ft long; and two plus one more for each additional 10 ft beyond 10 ft. The tiedowns must also meet the aggregate working load limit rule in 393.106.
What is the aggregate working load limit rule?
49 CFR 393.106(d) requires the tiedowns on an article to add up to at least one half its weight. A tiedown attached from the vehicle directly to the article, or passing over it and back to the same side, counts at half its working load limit. One that passes over or around the article to the other side of the vehicle counts at its full working load limit.
What working load limit does an unlabeled strap have?
If the maker did not mark it, use the default table in 49 CFR 393.108: 2 in synthetic webbing is 2,000 lb, 3 in is 3,000 lb and 4 in is 4,000 lb. Unmarked chain is treated as grade 30 proof coil, and unmarked wire rope gets one fourth of its nominal strength. Marked tiedowns use their marked value.
What forces must cargo securement withstand?
49 CFR 393.102 requires that forces stay below breaking strength at 0.8 g forward deceleration, 0.5 g rearward and 0.5 g lateral, and below working load limit at 0.435 g forward, 0.5 g rearward and 0.25 g lateral, applied separately. Loads not fully contained in the vehicle need a downward force of at least 20 percent of their weight.
Does the ratchet affect the strap's rating?
Yes. 49 CFR 393.108(a) defines a tiedown's working load limit as the lowest of any of its components, including the tensioner, or of the anchor points it attaches to. A strap rated higher than its ratchet or end hooks is only as good as the weakest part, so buy assemblies with a single marked rating.
Do these rules cover air shipments?
No. 49 CFR 393 Subpart I covers trucks and trailers on public roads. Air carriers and aircraft operators set their own cargo restraint requirements, and military airlift has separate rules. Get the carrier's requirements before designing the transport fixture, and check hazardous materials and export filing rules for the shipment.
Related
Sources
- eCFR: 49 CFR Part 393 Subpart I, Protection Against Shifting and Falling Cargo
- eCFR: 49 CFR 393.108 working load limit tables
- eCFR: 49 CFR 393.110 minimum number of tiedowns
- eCFR: 49 CFR 393.102 performance criteria
- eCFR: 49 CFR 393.104 standards for securement devices
- eCFR: 49 CFR 393.106 general securement requirements
Ready to
source it?
A person replies within 1 business day. NDA first.
Request a quote