Lifting Tongs are a scissor-style rigging tool that grips a load between two pivoted arms and lifts it with a hoist or crane. They solve the problem of moving objects that have no lifting eye, slot, or sling point — like steel plate, concrete blocks, hot ingots, or stacked lumber. The tongs convert vertical hoist tension into a horizontal clamping force at the jaws, and the harder you lift, the harder they squeeze. A 1-ton plate clamp with proper geometry will hold a 2,000 lb steel plate by friction alone with no slipping.
Lifting Tongs Interactive Calculator
Vary lifted weight, tong arm angle, and surface friction to see jaw clamp force and grip safety update live.
Equation Used
The article formula converts the lifted load W into one-jaw horizontal clamping force F using the included tong arm angle theta. The friction check compares available grip, mu times the total normal force from both jaws, against the lifted load.
- Symmetric two-arm lifting tong geometry.
- F is the normal clamping force at one jaw.
- theta is the included angle between tong arms at the pivot.
- Pivot losses, jaw pad deformation, and dynamic shock loading are not included.
The Lifting Tongs in Action
Lifting Tongs work on a self-energising principle. Two arms cross at a central pivot like scissors, with jaws at the bottom and a shackle or bail at the top. When you take a load on the hoist, the upward pull at the bail is reacted by the weight of the load pulling down through the jaws. That couple wants to rotate the arms about the pivot, and the only thing stopping it is the friction between the jaw pads and the load surface. The geometry is set up so the clamping force at the jaws is always proportional to the lifted weight — lift harder, clamp harder. That is why a properly designed tong does not need a screw, lever, or external power source.
The arm angle is the critical spec. If the angle between the arms (measured at the pivot) is too wide, the mechanical advantage drops and the jaws slip. Too narrow and the jaws can't open wide enough to bite a thick plate. Most plate clamps run a 30° to 60° included angle at rated load. The pivot pin must be a hardened shoulder bolt or clevis pin running in a bronze bushing or needle bearing — a worn pivot lets the arms cock sideways and the load tips out. Jaw pads are usually serrated hardened steel for raw stock, or urethane/copper for finished surfaces where you can't afford bite marks.
Failure modes are predictable. The most common is grease or mill scale on the load surface, which drops the coefficient of friction below the design value and the plate squirts out. The second is overloading past the rated capacity, which spreads the arms and pops the jaws clear. The third is using a plate clamp on material thinner than the jaw's minimum opening — the cam never engages and the clamp lifts with zero clamping force. Renfroe, Crosby IPU10, and Camlok CX series all spec a minimum jaw opening on the data plate for that reason.
Key Components
- Arms (legs): Two forged steel arms that cross at the central pivot. They transfer load from the bail at the top to the jaw pads at the bottom. Most rated tongs use SAE 4140 or equivalent forged alloy heat-treated to 28-32 HRC for toughness without brittleness.
- Central pivot pin: Hardened shoulder bolt or clevis pin running in a bronze bushing. Carries the full shear load from both arms — typically sized for a 5:1 design factor against the rated working load. Pin clearance must stay under 0.5 mm radial slop or the arms cock and the load tips.
- Jaw pads: Replaceable serrated steel inserts or urethane/copper faces. Serrated pads bite into mill-scale steel at roughly 0.4 coefficient of friction. Smooth urethane pads run 0.6+ on clean machined surfaces but mark soft material. Pads bolt on so you can swap them when the teeth round off.
- Bail / shackle: The single lift point at the top. Sized for the full rated capacity plus a 4:1 or 5:1 safety factor per ASME B30.20. A swivel bail is common on horizontal plate clamps so the clamp self-aligns under the hook.
- Locking cam (on plate clamps): A spring-loaded cam that holds the jaws on the plate before you take a load — keeps the clamp from falling off when you set it. The cam typically engages at 6 mm minimum plate thickness and disengages with a release lever when you set the plate down.
- Safety latch / lock-open lever: Mechanical detent that holds the jaws open during positioning and locks them closed during lift. Without it the rigger has to fight gravity to set the clamp on a vertical plate.
Industries That Rely on the Lifting Tongs
Lifting Tongs show up anywhere you need to move bulk material that wasn't designed with a lifting point. The pattern repeats across industries: pick raw stock, position it, release. The big design choices are jaw style (serrated for raw, smooth for finished), orientation (vertical plate clamp vs horizontal stack lifter), and rated capacity. Riggers who pick the wrong jaw style on a finished part end up with witness marks they can't polish out. Riggers who pick under capacity end up with dropped loads.
- Steel service centres: Crosby IPU10 vertical plate clamps lifting 1-inch A36 hot-rolled plate off a stack onto a CNC plasma table at a Russel Metals warehouse.
- Precast concrete: Renfroe Model J tongs handling 4,000 lb concrete barrier blocks at an Oldcastle precast yard, gripping the chamfered top edge.
- Forging and foundry: Heat-resistant ingot tongs picking 2,200°F billets out of a reheat furnace at a Scot Forge facility, with extended arms to keep the rigger clear of radiant heat.
- Lumber and panel: Caldwell Versa-Lift block tongs squeezing a banded unit of 2x10 SPF dimensional lumber off a flatbed at a Home Hardware distribution centre.
- Shipbuilding: Camlok CX horizontal plate clamps used in pairs on an overhead crane to lift 8 ft × 20 ft hull plate flat at a Seaspan Vancouver yard.
- Scrap and recycling: Heavy-duty drum tongs gripping crushed car bodies at a Schnitzer Steel scrap yard, where the jaws bite into ragged edges no sling could grab.
- Stone and slab: Abaco scissor clamps lifting 3 cm granite slabs at a stone fabricator running a Park Industries Voyager saw, with rubber pads to avoid edge chipping.
The Formula Behind the Lifting Tongs
The clamping force at the jaws is what determines whether the tong holds or slips. You compute it from the lifted weight, the geometry of the arms, and the coefficient of friction at the jaw face. At the low end of the typical operating range — a 30° included arm angle — the clamping force is high but the jaw opening is narrow, so you can't grab thick stock. At the high end — a 60° angle — the jaws open wide but the clamping force drops and you start needing serrated pads to keep the friction coefficient up. The sweet spot for most plate clamps lands near 45°, where you get a workable jaw opening and still develop roughly 1.2× the lifted weight as clamping force per side.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| Fclamp | Horizontal clamping force at one jaw | N | lbf |
| W | Weight of the load being lifted | N | lbf |
| θ | Included angle between the two arms at the pivot under load | degrees | degrees |
| μ | Coefficient of friction between jaw pad and load surface | dimensionless | dimensionless |
Worked Example: Lifting Tongs in a Renfroe-style plate clamp on hot-rolled steel
You are picking a 1,500 lb piece of 3/4-inch A36 hot-rolled steel plate off a stack with a vertical plate clamp on a 2-ton overhead bridge crane in a fab shop. The clamp has serrated hardened jaws and the manufacturer rates it for 30° to 60° arm angle under load. You want to verify the clamp will not slip on mill-scale plate where μ runs about 0.35.
Given
- W = 1500 lbf
- θnom = 45 degrees
- μ = 0.35 dimensionless
Solution
Step 1 — at the nominal 45° arm angle, compute the clamping force per jaw:
Step 2 — check the no-slip condition with μ = 0.35 on mill-scale steel:
Serrated jaws bite through the mill scale and effectively raise μ to about 0.55 because the teeth mechanically interlock with the surface, not just rub on it. Recheck:
Step 3 — at the low end of the typical arm angle, 30°, the clamp grips much harder but only opens to about 1/2 inch:
That is plenty of grip for thin plate, but if you tried to use this geometry on 1-inch stock the jaws would never close around it. At the high end of the range, 60°, the jaws open wide enough for 1-1/4 inch plate but clamping force collapses:
With serrated jaws that still gives 2 × 0.55 × 1,299 = 1,429 lbf of friction — under the 1,500 lbf load. At 60° on a 1,500 lb plate you are below the no-slip threshold and the plate will squirt out. That is why every rated plate clamp specifies a minimum AND maximum plate thickness on the data plate.
Result
Nominal clamping force per jaw is 1,810 lbf at 45°, giving a 1. 33× friction margin with serrated pads on mill-scale plate. At 30° the clamp generates 2,799 lbf per jaw — overkill for grip but only useful on thin stock — while at 60° it drops to 1,299 lbf and the plate slips on anything close to rated load. The 45° geometry is the sweet spot where jaw opening and grip both work. If you measure slip in the field at predicted-safe geometry, the three failure modes to check are: (1) oil or cutting fluid on the plate dropping μ below 0.3 — wipe the contact zone with solvent before you grip, (2) rounded jaw teeth from years of use — pull the pads and look for shiny worn tips instead of sharp serrations, and (3) a sprung pivot pin letting the arms cock so only one jaw makes full contact — measure the gap between arm faces with feeler gauges and compare against the manufacturer's wear limit, typically 0.5 mm.
When to Use a Lifting Tongs and When Not To
Lifting Tongs aren't always the right pick. The decision usually comes down to whether the load has a lifting point, how much surface marking you can tolerate, and how repetitive the lift is. Compare against slings and vacuum lifters on the dimensions that matter for production rigging.
| Property | Lifting Tongs | Chain or Web Sling | Vacuum Lifter |
|---|---|---|---|
| Load capacity range | 100 lb – 50 ton per clamp | 100 lb – 100+ ton | 50 lb – 20 ton |
| Setup time per pick | 3-5 sec, single rigger | 20-60 sec, often two riggers | 2-3 sec, single operator |
| Surface marking on finished parts | Yes — serrated jaws bite, urethane pads avoid this | Minimal with web slings | None on flat sealed surfaces |
| Works on porous or rough material | Yes — concrete, scale, rough cuts | Yes — anything you can wrap | No — needs sealed flat surface |
| Power required | None — self-energising | None | Compressed air or electric vacuum pump |
| Sensitivity to load weight estimate | High — under-loaded clamps don't engage cam | Low | Moderate — must stay under pad rating |
| Typical service life | 10+ years with pad replacement every 2-5 years | 1-3 years for web slings, 5+ for chain | 5-10 years, seal kits every 1-2 years |
| Cost per rated ton | $300-$800/ton | $50-$200/ton | $2,000-$5,000/ton |
Frequently Asked Questions About Lifting Tongs
The locking cam isn't seating before you take tension. On a Crosby IPU10 or Renfroe vertical plate clamp, the spring-loaded cam needs the rigger to push the clamp fully down onto the plate edge so the cam rotates into the lock-on position. If you hang the clamp on the plate and start lifting before the cam clicks, the jaws float open during initial tensioning and the plate slides out a few inches before the geometry self-energises. The second lift works because the cam is now in position from the first attempt.
Fix: listen for the audible click or feel the lock-on lever drop into the engaged detent before you call for tension. On a tall plate, tap the top of the clamp with a dead-blow hammer to fully seat it.
No, and this is one of the most common dropped-load incidents in steel yards. A vertical plate clamp is designed for the load line to pull straight up through the bail with the plate hanging below in line with the jaws. Lift a plate flat with one vertical clamp and the load tries to pivot the clamp 90° about the jaws — the geometry that creates clamping force disappears, the cam disengages, and the plate falls.
For flat picks you need either a dedicated horizontal plate clamp like a Camlok TBC, or two vertical clamps used in a properly rigged spreader-bar configuration with the load line at the angle specified by the manufacturer (usually within 30° of vertical).
Don't pick the clamp by max load alone — check the working load range on the data plate. Most plate clamps spec both a maximum AND a minimum rated load. Below the minimum (often 10-20% of WLL) the cam spring isn't strong enough to develop clamping pressure on its own, and a 200 lb plate in a 2-ton clamp can slip even though you're nowhere near capacity.
For a wide load range, run two clamps: a 1/2-ton for light picks and a 2-ton for heavy. Trying to cover 10:1 with one clamp will bite you on the small end.
Plate hardness. Hot-rolled A36 runs about 120 HBN — the serrated jaws hit roughly 30-35 HRC (around 300 HBN), so they bite a clear tooth pattern roughly 0.5-1 mm deep. On AR400 abrasion-resistant plate at 380+ HBN, the jaws can't penetrate the surface and only scratch it. The clamping force is identical, but you've lost the mechanical interlock from teeth-in-material and you're relying on pure friction, which drops the effective μ from ~0.55 to ~0.35.
If you're regularly lifting AR plate or quenched-and-tempered stock, derate the clamp by about 30% or switch to a higher-capacity unit.
Choose tongs when cycle time matters more than load variety and the load has a consistent grip surface. A rigger with a plate clamp picks a piece in 3-5 seconds versus 30+ seconds for a sling. Compared to a magnet, tongs work on non-ferrous material (concrete, stainless, aluminium) and don't drop the load if power fails.
Pick a sling instead if loads vary wildly in shape, or a magnet if you need zero surface marking on flat ferrous stock and have reliable power. Tongs are the right call for repetitive picks of similar parts — steel service centres, precast yards, and sawmills all run them for that reason.
Derating helps for moderate contamination but doesn't save you on heavy oil or coolant. The friction coefficient on an oily mill-scale surface can drop to 0.10-0.15, and no amount of derating gets you above the no-slip threshold because the clamping force scales with the load you're trying to lift — the ratio stays the same.
The fix is mechanical, not numerical: wipe the grip zone with a rag and solvent (a 4-inch band along the lift edge is enough), or switch to a clamp with deeper, sharper serrations that can cut through the oil film to bare metal. Renfroe and Camlok both publish μ values for clean vs oily surfaces in their engineering data — use those numbers, not a generic 0.35.
B30.20 covers below-the-hook lifting devices, which includes engineered tongs, and allows a 3:1 to 4:1 factor on structural members because the device is designed, tested, and rated as an integrated unit with a known load path. General rigging hardware (shackles, hooks) uses 5:1 because the user combines them in unpredictable ways and field abuse is more likely.
The practical consequence: never load a plate clamp past its WLL stamp. There's less margin built in than on a shackle of the same rated capacity, and overload is the leading cause of arm failure on tongs. If you suspect a clamp has been overloaded, take it out of service and have it proof-tested at 125% before returning it to the rack.
References & Further Reading
- Wikipedia contributors. Tongs. Wikipedia
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