01
What a cheek plate does, and where it stops
It puts more steel at the hole and nowhere else. Everything about the decision follows from where the governing check lives relative to that patch of steel.
A cheek plate is a doubler: a disc or a shaped plate welded to each face of the main plate, concentric with the pin hole, drilled through with it. Its purpose is to make the plate locally thicker where the pin bears.
Three checks respond, and they respond very differently.
Bearing improves in proportion to the added thickness. The pin bears on all three plates through the full depth of the hole. If the cheeks are properly fitted and their welds develop them, the bearing area really is the combined thickness times the pin diameter.
Net-section tension improves, with a condition. The net section is taken across the pin, where the cheeks are present. It only counts if the cheeks are developed on both sides of that section by enough weld to carry their share into them.
Shear-out barely improves. The planes run from the edge of the hole out to the free edge, and a cheek helps only over the part of that run it physically covers. A cheek whose radius stops short of the free edge leaves the outer end of each plane at the main plate thickness, and the outer end is the part that governs, so the check moves far less than the added steel suggests.
The weld at the base does not improve at all. It is nowhere near the cheeks.
02
What the engine can and cannot tell you here
The shipped pack models a single plate and has no cheek plate input, so it cannot check one directly. What it can do is bracket one, and the bracket is the engineering point.
Run the same lug twice.
The two runs that bracket a cheeked lug
- is the main plate thickness
- is one cheek plate's thickness
At the main plate thickness. Every check is correct except bearing and net section at the hole, which are conservative because the cheeks are really there.
At the combined thickness. Bearing and net section are now correct, and every check that depends on material beyond the cheek's extent is optimistic, because that material is not there.
A real cheeked lug sits between those two runs, and it is not in the middle. It is at the combined-thickness answer for the checks at the hole, and at the main-plate answer for everything else.
Lifting Lug Calculator
Full sizeOpen these inputs
| Check | Main plate alone | Combined thickness | Which is the truth |
|---|---|---|---|
| Pin bearing on the lug | 75.0% | 38.3% | combinedThe pin bears on all three plates at the hole, so the full combined thickness is genuinely there. |
| Net-section tension | 38.3% | 19.5% | combinedThe net section is taken at the pin, where the cheeks are present, provided they are developed either side of it. |
| Double-plane shear-out | 108.4% | 55.3% | main plateThe shear-out planes run to the free edge. A cheek helps only over its own extent, and it is usually not that big. |
| Fillet weld throat resultant | 71.7% | 63.2% | main plateThe weld group is at the base of the main plate. Cheeks at the hole are nowhere near it. |
Read the third and fourth columns together and the design fails. Bearing is genuinely 38.3 percent, which is comfortable. Shear-out is genuinely 108.4 percent, which is not. A reader who took the combined-thickness run as the answer would see 55.3 percent and ship it.
03
The worked case, both ways round
A 420 kN lift point on 25 mm plate with two 12 mm cheeks. The cheeks fix the check that was not the problem.
Lifting Lug Calculator · computed at page render
The main plate alone: 25 mm
The lower bound. Correct for shear-out and for the weld; conservative at the hole.
| Design load | 420.0kN |
|---|---|
| Double-plane shear-outcorrect as it stands - failed | 108.4% |
| Pin bearing on the lugconservative: the cheeks are really there | 75.0% |
| Net-section tensionconservative for the same reason | 38.3% |
| Fillet weld throat resultantcorrect: the cheeks are nowhere near it | 71.7% |
Shear-out fails, and adding cheek plates does not change that number. This is the run that tells you whether the cheeked design works, for the check that governs.
Open this example in the calculatorLifting Lug Calculator · computed at page render
The combined thickness: 49 mm
The upper bound. Correct at the hole; optimistic everywhere the cheeks do not reach.
| Pin bearing on the lugagainst 75.0% on the main plate alone - this one is real | 38.3% |
|---|---|
| Net-section tensionreal, provided the cheeks are developed either side | 19.5% |
| Double-plane shear-outnot real: the planes run past the cheek | 55.3% |
| Fillet weld throat resultantnot real: the weld is on the main plate | 63.2% |
Everything passing, and two of these four numbers describe a lug that does not exist. This is the run that flatters a cheek plate, and it is the one somebody will screenshot.
Open this example in the calculatorLifting Lug Calculator · computed at page render
One 40 mm plate instead
No cheeks. A single thicker plate, which raises every check at once because the material is everywhere.
| Double-plane shear-outagainst 108.4% on 25 mm | 67.8% |
|---|---|
| Pin bearing on the lug | 46.9% |
| Net-section tension | 23.9% |
| Fillet weld throat resultant | 66.1% |
Passing everywhere, with one plate, one pair of welds and one set of surfaces to inspect. On this lift the cheek plate was the wrong answer for one reason: shear-out was governing, and shear-out is the check cheeks do least for.
Open this example in the calculator04
When a cheek plate is worth fitting
When bearing governs and thickening the whole plate is expensive. That is a narrower window than the frequency with which cheek plates get drawn.
Fit them when bearing governs. Then they are efficient: material exactly where the check is, and the rest of the plate stays thin.
Fit them when the plate is already at a stock thickness. Going from 40 mm to 50 mm plate can mean a different material order, a different lead time and a different weldability conversation. Two 12 mm cheeks off an offcut can be quicker.
Fit them when the shackle demands a wide jaw. A cheeked lug can be locally thick at the hole and thin elsewhere, which sometimes fits a shackle a uniformly thick plate would not.
Do not fit them to fix shear-out. They do not, unless the cheek extends past the free edge, and a cheek that big is a plate.
Do not fit them to fix the weld. They are at the wrong end.
Do not fit them where inspection is hard. Two extra welds, a crevice between the plates, and a geometry that traps water. On an outdoor or marine lug that is a maintenance liability with no structural return unless bearing was the problem.
If you are fitting cheek plates
- 01Confirm bearing is the governing checkIf it is not, they are the wrong intervention and something else is.
- 02Check shear-out on the main plate aloneCheeks do not help beyond their own extent, so the bare plate is the honest number.
- 03Develop the cheeks into the main plateEnough weld either side of the net section to carry each cheek's share, not a token seal run.
- 04Drill the hole after weldingSo all three plates are concentric. A cheek 2 mm off centre is a bearing area that is not what the calculation used.
- 05State the cheek diameter and thickness on the drawingWith the weld detail. They are structural components and they need dimensions.
- 06Consider whether one plate is simplerCompare on total cost including welding, inspection and the crevice, not on steel weight.
05
Six ways cheek plates go wrong
Four are about crediting them where they do not act.
1. Credited for shear-out. They act over their own extent, and the shear-out planes usually run past it.
2. Credited for the weld. They are at the hole and the weld is at the base.
3. Not developed into the main plate. A cheek attached with a seal run is a cheek that cannot carry its share, and the combined thickness is then a fiction.
4. Fitted where bearing was never the problem. Cost, welding, inspection and a crevice, in exchange for improving a check that had margin.
5. Drilled before welding. Three plates whose holes are not concentric bear on a smaller area than any of the three calculations assumed.
6. Left off the drawing as a detail. They are structural components with a diameter, a thickness and a weld, and a drawing that shows them as a circle with no dimensions has not specified them.
Common questions
- What does a cheek plate on a lifting lug actually do?
- It makes the plate locally thicker at the pin hole, which raises the bearing area and the net section at the pin. It does very little for shear-out, because the shear-out planes run from the hole to the free edge and a cheek only helps over its own extent. It does nothing at all for the weld at the base of the lug, which is nowhere near it. That distribution of benefit is the whole decision.
- When should I use a cheek plate instead of a thicker plate?
- When bearing is the governing check, which is when the extra material is exactly where the problem is. Also when the main plate is already at a convenient stock thickness and going up a size means a different order and lead time, and where a shackle needs a locally thick hole in an otherwise thin plate. If shear-out or the weld governs, a cheek plate does not address it and a thicker plate does.
- Can a cheek plate fix a failing shear-out check?
- Only if it extends past the free edge, and a cheek that big is a plate. In this article's worked example the main plate alone fails shear-out at 108 percent, and the combined-thickness run reports 55 - a number that describes a lug that does not exist, because the shear-out planes run out past the cheek. Reading the combined run as the answer would ship a failing lug, and the same lift is solved by a single 40 mm plate at 68 percent.
- How should cheek plates be welded and drilled?
- Welded with enough weld either side of the net section to develop each cheek's share into the main plate - a seal run is not a structural attachment, and without development the combined thickness is a fiction. Drilled after welding, so all three plates are concentric: a cheek two millimetres off centre gives a bearing area smaller than any of the three calculations assumed. Both the cheek's diameter and thickness and the weld detail belong on the drawing as dimensions.
- Are there downsides to cheek plates?
- Two extra welds that have to be developed and inspected, two more surfaces, and a crevice between the plates that traps water. On an outdoor or marine lug that is a real maintenance liability, and none of it appears in a utilisation. Where bearing was not the governing check, that cost buys nothing structurally, which is what makes an unnecessary cheek plate decoration with an inspection bill attached.
Sources
Every document below is linked at its publisher or regulator. Xarpis reproduces no standard text; where a clause is named, the identifier is given so you can find it in your own copy.
ASME BTH-1Design of Below-the-Hook Lifting Devices
ASME · paid document
Structural, mechanical and electrical design criteria for below-the-hook lifting devices, used alongside ASME B30.20 which carries the safety requirements. The current edition is BTH-1-2023; Xarpis implements the 2020 edition and says so on every result.
EN EurocodesEurocodes: Building the future
European Commission, Joint Research Centre · free portal
The Commission's own Eurocodes portal: the structure of EN 1990 to EN 1999, the database of Nationally Determined Parameters, and the second-generation timetable. The standards themselves are sold by the national bodies, but the NDP database is free and is what decides which partial factors apply in your country.
ASME B30.26Rigging Hardware
ASME · paid document
Shackles, links, rings, swivels, turnbuckles, eye bolts, hoist rings and load-indicating devices: identification, effect of environment, inspection and removal criteria. The volume that governs the pin your padeye is designed around.
ANSI/AISC 360Specification for Structural Steel Buildings
American Institute of Steel Construction · free to read
The US steel design specification, in both LRFD and ASD. AISC publishes it for free download, which makes it one of the few structural standards a reader can check the same afternoon they read about it.
Run the check properly
Reading about a calculation is not the same as being able to hand one over. These tools produce the traceable record.
Something here wrong, or thinner than it should be? Tell us which paragraph and it gets rewritten. Articles carry the date they were last revised for exactly this reason.