Calculation
dShear = √(4F/(m·π·τallow)); dBearing = F/(pallow·l)
There is no single universal pin-diameter formula: depending on geometry, shear, bearing or, separately, bending can govern.
dScher = √(4F/(m·π·τzul)); dPressung = F/(pzul·l)
Required pin diameter against shear and bearing
There is no single universal pin-diameter formula: depending on geometry, shear, bearing or, separately, bending can govern.
MINTSI
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Result
Select a target and calculate.
Understand the inputs
- Shear-governed diameter dShear — Minimum diameter so the allowable shear stress is not exceeded.
- Bearing-governed diameter dBearing — Minimum diameter so the allowable bearing pressure is not exceeded.
- Joint force F — Transverse force to be transmitted through the pin.
- Shear planes m — 1 for single shear, 2 for double shear.
- Allowable shear stress τzul — Material-dependent shear stress limit from reference values or standard.
- Allowable bearing pressure pzul — Material-dependent bearing pressure limit; markedly lower for sliding fits in joints than for press-fit pins.
- Effective bearing length l — Rod eye: its own thickness; fork: sum of both leg thicknesses.
Example
5,000 N, double shear, τallow = 60 MPa, pallow = 40 MPa and a 20 mm bearing length give dShear ≈ 7.3 mm and dBearing = 6.25 mm; the larger value governs, rounded up to the next standard size, e.g. 8 mm.
Assumptions and limits
Pure pre-sizing without a bending check; a slender pin with a large fork-to-rod gap can fail in bending despite adequate shear and bearing sizing, and must additionally be checked with the clevis pin bending calculator.
Understand Required pin diameter against shear and bearing
This calculator finds the required pin diameter against both shear and bearing failure; the larger of the two values governs.
What does this quantity describe?
From allowable shear stress τallow, the shear-critical minimum diameter follows as dShear = √(4F/(m·π·τallow)); from allowable bearing pressure pallow, the bearing-critical minimum diameter follows as dBearing = F/(pallow·l). Both are computed separately; the diameter actually chosen is the larger of the two, rounded up to the next available standard size.
This is like selecting a cable cross-section that must satisfy both a current-carrying limit and a voltage-drop limit: the minimum cross-section is computed separately for each requirement, and the larger one is chosen to satisfy both criteria simultaneously.
Formula and variables
dShear = √(4F/(m·π·τallow)); dBearing = F/(pallow·l)
dShear = √(4F/(m·π·τallow))dBearing = F/(pallow·l)chosen: d = max(dShear, dBearing), rounded up
| Symbol / input | Meaning |
|---|---|
| Shear-governed diameter dShear | Minimum diameter so the allowable shear stress is not exceeded. |
| Bearing-governed diameter dBearing | Minimum diameter so the allowable bearing pressure is not exceeded. |
| Joint force F | Transverse force to be transmitted through the pin. |
| Shear planes m | 1 for single shear, 2 for double shear. |
| Allowable shear stress τzul | Material-dependent shear stress limit from reference values or standard. |
| Allowable bearing pressure pzul | Material-dependent bearing pressure limit; markedly lower for sliding fits in joints than for press-fit pins. |
| Effective bearing length l | Rod eye: its own thickness; fork: sum of both leg thicknesses. |
Choose the inputs correctly
Force F, shear planes m and allowable shear stress τallow set dShear; force F, allowable bearing pressure pallow and effective bearing length l set dBearing.
How to use the calculator
Enter force, shear configuration and allowable shear stress to get dShear, and allowable bearing pressure and bearing length for dBearing. Choose the larger of the two for the design and round up to the next available standard size.
Worked example
5,000 N, double shear, τallow = 60 MPa, pallow = 40 MPa and a 20 mm bearing length give dShear ≈ 7.3 mm and dBearing = 6.25 mm; the larger value governs, rounded up to the next standard size, for example 8 mm.
Understand the result and units
dShear exceeding dBearing shows that shear failure sets the minimum size in this example. After choosing a standard diameter (8 mm here), bending stress should additionally be checked with the clevis pin calculator, since this pre-sizing does not include bending.
Force is given in N, allowable stresses and pressures in MPa, bearing length in mm, and the resulting diameters in mm.
Why there is no single pin-diameter formula
A pin can fundamentally fail in three independent ways: shear, bearing (at fork or rod), and bending. Which of these three mechanisms governs for a given geometry depends on the ratio of diameter to bearing length and to the distance between load-introduction points, and cannot be predicted in a blanket way. A complete pin design therefore always computes all three minimum diameters separately and chooses the largest, rather than relying on a single simplified formula.
Typical applications
The calculation is used as a first step in pin sizing, to quickly find a rough minimum size for a given load and material combination before a final standard size is chosen and fully verified.
Assumptions, limits and common mistakes
This pre-sizing covers only shear and bearing. A slender pin with a large fork-to-rod gap can fail in bending despite adequate shear and bearing sizing; this must additionally be checked with the clevis pin bending calculator before the final diameter is set.
Common mistake: A common mistake is checking only one of the two requirements and overlooking the other. It is also easy to skip the bending check entirely, even though it is often the actually governing requirement for slender pins and can demand a larger diameter than shear or bearing alone.
Frequently asked questions
Which diameter do I choose if dShear and dBearing differ?
Always the larger of the two, rounded up to the next available standard size.
Why isn't the bending check included here?
Because it needs additional geometry inputs (fork-leg thickness, rod-eye width) deliberately kept separate in a compact pre-sizing tool; use the clevis pin bending calculator for that.
Where do I get allowable shear stress and bearing pressure?
From material reference tables for the pin and component materials, depending on load type and chosen safety factor; see technical literature or manufacturer data.
What if no standard diameter fits exactly?
Always choose the next larger available standard size, never a smaller one, even if the computed value sits closer to the smaller size.
Is this pre-sizing enough for the final design?
No, it is a first step; bending stress must additionally be checked and the chosen standard size fully verified.