Clevis pin load capacity cannot be determined from pin diameter and a double-shear calculation alone. Check pin shear, bearing stress in the eye and fork ears, pin bending, and the strength of the surrounding connection. Each result needs its own geometry, loading assumptions and material basis.
The useful starting point is a drawing of the complete joint. Two connections using the same 10 mm pin can place different demands on the pin and fork because their contact widths, gaps and load paths differ. This guide explains the initial calculations, provides a shear and bearing stress calculator, and shows why reducing one stress does not necessarily reduce another.
Define the clevis joint and its load path
What is a clevis, and where do the lug and pin fit?
A clevis is a fork-shaped connector with two ears. A central eye or tang fits between those ears, and a pin passes through the aligned holes. In a lug and clevis connection, identify the central lug separately from the two fork ears so that its thickness, material and applied load remain clear.
The working force considered here acts transverse to the pin axis. The central member loads the pin, and the two ears react that load into the fork body. The retaining arrangement prevents pin withdrawal according to its design; it is a separate interface from the transverse load path.
Identify single shear and symmetric double shear
In the symmetric double-shear model, the central load is shared by two identical ears and passes through two pin sections between the eye and the ear contacts. Each section carries half the total transverse force. A single-shear arrangement has one resisting section for the assumed force.
Count the sections from the load path, rather than from the number of holes visible in a photograph. Unequal ear stiffness, eccentric loading, gaps and distorted contact can invalidate equal load sharing. Two nominal shear planes do not establish twice the allowable load for the complete joint.
Gather the geometry, material and loading inputs
Separate catalogue dimensions from design allowables
Record pin diameter, each ear’s effective contact thickness, central eye thickness, side gaps, hole dimensions and the material remaining around each hole. Identify the actual surfaces that carry load. A relieved edge or a bushing can make the effective contact geometry different from the overall part envelope.
Dongzhou’s PC catalogue identifies PC pins for FK and FT clevis joints. Its PC10 row lists d1 = 10 mm, d3 = 3.2 mm, L1 = 29 mm and L2 = 24.5 mm. These fields help identify the component; they do not provide the ear thickness, eye thickness or allowable load of an unspecified assembly. Confirm each length endpoint on the drawing before using it in a model.
ISO 2341:1986 describes headed metric clevis pins, including types with and without a split-pin hole. Product identity and dimensions are different from an assembly load rating. Use the clevis dimension guide to reconcile the interfaces before selecting calculation inputs.
Specify the load case and material condition
Define the force being checked: its magnitude, direction, application point and whether it is steady, reversing, repeated or subject to impact. Cylinder force, linkage geometry and an external load may need to be assessed together. A normal operating force is not automatically the maximum design force at every position.
The pin, fork and central eye need separate material definitions. Specify grade, heat-treatment condition, surface treatment and the applicable strength or allowable-stress data. “Steel” is not a design allowable. Neither is a catalogue list of material options proof of the condition of a particular supplied part.
I would review the assembly section, load direction, contact widths and gaps before selecting the pin diameter. I would also ask for the material and heat-treatment condition of the pin, fork and central eye separately, because a low average pin shear stress does not establish the strength of the complete connection.
Calculate average pin shear stress
Use the resisting area and number of shear planes
For a solid circular section of diameter d, the gross area is A = πd²/4. With transverse force F and n equally loaded resisting sections, the average shear stress is:
τavg = F / (nA) = 4F / (nπd²)
Use n = 1 for the assumed single-shear case and n = 2 for symmetric double shear. In the latter, F is the total applied force, not the force on each ear. Substituting F/2 and then dividing by two again would understate the result.
Enter F in newtons and dimensions in millimetres to obtain stress in N/mm², equivalent to MPa. Use diameter, not radius. The expression assumes a complete solid circular resisting section; a cross-hole, groove, thread or hollow section in the evaluated region needs an appropriate section and stress model.
Distinguish stress, strength and allowable load
Pin shear stress is the calculated demand. Material shear strength or an applicable shear allowable is the resistance against which that demand is assessed. Yield strength, ultimate strength and design allowable values have different meanings. Keep the design basis and safety factors with the value being used.
If an appropriate average shear allowable τallow is established, nAτallow describes the load limit for this simplified shear check. It does not account for bending, bearing, the surrounding parts or the other service requirements. The average result also differs from a local peak-stress result.
A bolt shear strength calculator may use a similar area expression, but the connection still needs the correct model. Threads at the shear plane, clamping, slip and bearing conditions can change the assessment. Also distinguish a load-transmitting clevis pin from a sacrificial shear pin deliberately designed to fail for machinery protection.
Calculate bearing stress in the lug and clevis ears
Use projected area for the average bearing check
For the central eye of effective bearing thickness b, the simplified projected area is db. For two identical ears of effective thickness a, each ear carries F/2 over projected area da. The corresponding average values are:
peye = F / (db)
pear = F / (2da)
Here, bearing stress means the average compressive loading on projected pin-hole contact area. It is not a rolling-bearing load rating and is not the peak contact pressure around the bore. Autodesk’s clevis pin calculation documentation separates central-member bearing, clevis bearing, pin shear and pin bending checks.
Check each member against its own requirements
Do not use the pin’s shear allowable as a bearing allowable for the fork or eye. Different members can have different materials, treatments and failure criteria. Where a bushing is present, assess the interfaces and installation requirements that the bushing design introduces.
Thicker ears reduce F/(2da) when force and pin diameter remain fixed. They do not reduce the central eye value F/(db) unless its relevant dimensions or load also change. This distinction matters when an apparently stronger fork leaves the eye as the limiting member.
Check pin bending and the effect of the contact geometry
Define the model before calculating the moment
A pin spans contact regions rather than carrying only a mathematical shear force. Find the bending moment from the actual support and loading model, then use the section properties. For a complete solid round section under an appropriate elastic beam model:
σb = M / Z = 32M / (πd³)
Use M in N·mm and d in mm for MPa. The total pin length is not automatically the support span or moment arm. Head length, retaining projection and unused shank do not all define the bending geometry.
For the particular symmetric model with uniform bearing load over the central thickness b and each ear thickness a, and zero side gap, the centre-section moment is:
Mcentre = F(b + 2a) / 8
This is the idealized geometry shown in the Autodesk method, expressed here with metric inputs. Side gaps, nonuniform contact, unequal reactions or a different support model require a revised moment calculation. Do not import this coefficient into a different assembly without checking those assumptions.
A low average shear stress does not complete the design
A NASA-sponsored report on lattice-block test fixtures separately calculates shear and bending for its particular clevis pin. Its material values and stress definitions belong to that fixture. The useful lesson is the separate checks, not a transferable load rating.
Where combined stress, fatigue or local contact governs, use the evaluation method appropriate to the material and application. Comparing a nominal average stress with an unrelated peak-stress criterion can be as misleading as omitting a failure mode entirely.
Worked example and shear and bearing stress calculator
Start with explicit assumed inputs
Consider an illustrative industrial clevis connection carrying a 5 kN transverse load. Assume a solid 10 mm pin, an 8 mm central eye and two 4 mm ears sharing the force equally. These are calculation inputs, not PC10 test data or an assembly rating. The pin’s gross section area is 78.54 mm².
| Quantity | Calculation | Result |
|---|---|---|
| Average double-shear stress | 5,000 / (2 × 78.54) | 31.83 MPa |
| Average eye bearing stress | 5,000 / (10 × 8) | 62.50 MPa |
| Average bearing stress in each ear | 2,500 / (10 × 4) | 62.50 MPa |
The corresponding ideal single-shear average would be 63.66 MPa if the same total force acted across one complete section. That comparison changes the assumed resisting area; it does not demonstrate that a physical single-shear conversion retains the original bending or contact conditions.
Compare thicker ears across more than one check
Increasing each ear thickness from 4 to 6 mm reduces average ear bearing stress from 62.5 to 41.7 MPa, a 33.3% reduction under the same load. Eye bearing stress remains unchanged. Thin ears can be susceptible to bearing deformation or hole elongation, depending on their material and geometry; the calculated stress alone does not establish that either arrangement will fail or pass.
Now apply the zero-side-gap bending model defined above to both assumed arrangements. Keep F, d and b unchanged, and let each ear’s effective contact thickness a increase. The wider support-contact zones move their load resultants farther from the centre. In this model, the pin’s nominal bending stress increases even though the ears’ average bearing stress decreases.
| Model result | a = 4 mm | a = 6 mm |
|---|---|---|
| Average pin double-shear stress | 31.83 MPa | 31.83 MPa |
| Average eye bearing stress | 62.50 MPa | 62.50 MPa |
| Average bearing stress per ear | 62.50 MPa | 41.67 MPa |
| Centre bending moment, F(b + 2a)/8 | 10,000 N·mm | 12,500 N·mm |
| Nominal pin bending stress | 101.86 MPa | 127.32 MPa |
This is not a recommendation to reduce ear thickness. It shows why a geometric change needs a complete reassessment, including pin length and actual contact conditions. Material grade, heat-treatment condition and applicable design allowables must be specified for each member before drawing a strength conclusion.
Average double-shear and bearing stress calculator
Use positive values for total transverse force F, solid pin diameter d, central eye thickness b and each identical ear thickness a. The calculator assumes two symmetric load paths, a complete solid circular pin section and effective projected bearing areas. It reports calculated average stresses, not allowable load, fatigue life or a pass/fail result. Pin bending and the other joint checks remain separate.
The static example above shows the calculation. Enable JavaScript to calculate other inputs.
| Output | Value |
|---|---|
| Gross pin section area | mm² |
| Average pin double-shear stress | MPa |
| Average central eye bearing stress | MPa |
| Average bearing stress in each ear | MPa |
For an economic comparison, assume a revised assembly costs 40% more per replacement event, including parts, labour and downtime. It then needs 1.4 times the service life to break even on replacement cost per operating cycle. If equivalent-duty testing subsequently demonstrates twice the life, that cost falls by 30%, assuming event costs remain unchanged. No life multiplier follows from a reduction in bearing stress alone.
Check the rest of the joint before stating load capacity
Review the lug, fork and surrounding connection
The hole leaves a reduced net section in the eye and ears. Hole edge distance, local bending, possible tear-out and the fork body or rod-side attachment need their own checks. Increasing pin diameter can reduce some nominal pin stresses while removing material from the surrounding members.
Only compare limiting loads expressed on a consistent load basis, with compatible design criteria and the required interactions accounted for. Taking the smallest number from unrelated ultimate, yield and allowable-stress calculations does not produce a coherent assembly rating.
| Item | What the review needs | What does not establish it |
|---|---|---|
| Pin bending and local contact | Contact widths, side gaps, reactions, section geometry and model | Nominal diameter alone |
| Eye and ear strength | Effective thickness, net section, edge geometry and material condition | A satisfactory pin shear result |
| Retention | Specified pin-retainer interface and applicable axial requirements | A transverse shear calculation |
| Repeated or reversing service | Applicable fatigue, wear and duty requirements | A static stress screen or material certificate alone |
Keep axial retention separate from transverse strength
Dongzhou describes the dished PM-K retainer as maintaining tension to reduce rattling. That axial function does not establish the transverse working load of the pin, fork and eye. The retention guide addresses the separate hole, groove and clip interfaces.
A material certificate confirms specified material information within its scope. It is not an assembly fatigue test. Similarly, a dimensional standard is not evidence that a particular combination has been tested at the intended load and duty.
Specify the PC pin and FK/FT connection for review
Send the assembly section, load cases and required evidence
A useful enquiry identifies the components to be supplied and provides the drawing revision, actual contact widths, side gaps, pin and bore dimensions, material conditions, load cases, environment and retaining arrangement. State the required inspection, material records or validation evidence rather than asking only for a “stronger pin.”
For PC pins with FK or FT clevises, confirm the intended combination and interfaces. The complete clevis and pin selection guide covers the matching geometry, while the materials and finishes guide helps define the component conditions.
Organize the review before placing the order
Use this sequence to prepare a clevis connection for technical review. It organizes inputs and evidence; it does not replace the applicable design approval or test requirements.
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Define the assembly and load cases
Identify the pin, ears, central member, retaining parts and rod-side attachment. Record the load direction, magnitude and duty conditions with the drawing revision.
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Record geometry and material condition
Specify effective contact thicknesses, side gaps, pin and hole dimensions, edge geometry, material grades and relevant treatments for each member.
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Select the models and design criteria
Document load sharing, resisting sections, contact assumptions, allowable values and their sources. Keep shear, bearing, bending and other failure-mode criteria distinct.
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Review the complete connection
Compare the calculated demands with the applicable resistance criteria and evaluate the remaining joint, retention and service requirements. Identify further analysis or testing where needed.
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Define the supply and evidence scope
List the components, controlled specifications, inspection records and validation evidence required for the enquiry, with responsibility for the final technical disposition.
I would keep the calculation assumptions beside the drawing revision when sending an enquiry. If the proposed change alters ear thickness, eye width or pin contact length, I would return it for a joint review rather than approving it from the pin shear result alone. The drawing and sample RFQ guide sets out the component information to provide.
Questions about clevis pin strength calculations
Is a clevis pin always in double shear?
No. Determine the resisting sections from the actual load path. The symmetric double-shear calculation assumes two suitable sections and equal reactions at the two ears. A different arrangement, eccentric load or unequal contact needs its own assessment.
Does double shear mean twice the load capacity?
It doubles the ideal resisting area compared with one identical complete section sharing the same assumed allowable. It does not automatically double the capacity of the complete connection, which also depends on bearing, pin bending, the surrounding members and the service requirements.
Can I use a bolt shear strength calculator for a clevis pin?
Only use a calculation whose section, load sharing and connection assumptions match the evaluated pin. Threaded sections, cross-holes, grooves, clamping and slip conditions can require different treatment. A bolt calculator result does not establish the strength of a clevis assembly.
What is the difference between bearing stress and shear stress?
Average pin shear stress divides transverse force by the resisting pin-section area. Average bearing stress divides a member’s force by the projected pin-hole contact area. They describe different demands and require appropriate criteria for the material and member being checked.
Can pin diameter alone determine a safe working load?
No. The connection also requires defined loading, contact geometry, material condition, retaining arrangement and applicable design criteria. A diameter-only stress calculation cannot account for the complete joint or establish its fatigue life.
Why check bending when average pin shear stress is low?
Shear and bending are separate demands. Contact widths, gaps and reaction locations determine the pin’s bending moment. A low average shear result does not show that bending, local contact or the surrounding components satisfy their requirements.
For a PC pin and FK/FT clevis component enquiry, send the assembly drawing, load cases, required material conditions and supply scope to Ningbo Dongzhou Transmission Co., Ltd. at sale02@hkdongzhou.com, or use the contact page. The website customer-service hotline is +86-574-87815807.
Keep calculated demand, material resistance and the conditions outside the model visible in the same review. That makes a change in pin diameter or ear thickness a traceable engineering decision and gives the supplier a clearer component specification.
