To identify the right size split cotter pin, you must match the nominal diameter of the pin to the diameter of the drilled hole, and ensure the effective length is long enough to bend after passing completely through the assembly.
Split cotter pins (governed by standards like DIN 94) are uniquely sized by the hole they are fitting into, not the actual width of the wire
1. Determine the Diameter
- Measure the Hole: Use a vernier caliper, drill bit, or pin gauge to measure the inside diameter of the hole you are trying to fill.
- Match the Nominal Size: If your hole measures 4 mm, you need a 4 mm nominal split pin.
- The Manufacturer’s Clearance: Do not worry if the actual wire thickness feels slightly smaller when you measure it with calipers. Under DIN 94 Standards, the actual pin diameter is manufactured undersize so it slides through the hole smoothly without lateral play.
- Avoid Under-Sizing: Never use a pin that is too small for the hole. Vibration will cause a loose pin to wear the hole into an oval shape over time, leading to eventual mechanical failure.
2. Determine the Effective Length
- Measure the Component Thickness: Measure the total distance the pin needs to travel (e.g., the width of the shaft or the distance through a castle nut).
- Account for the Prongs: The “effective length” of a split pin is measured from the underside of the loop (the head) to the tip of the shortest leg.
- Add Clearance for Bending: Choose a length where both legs extend past the exit hole by at least the thickness of the pin’s diameter. This ensures you have enough leverage to bend the tines back securely with pliers.
You can order these parts in Mild Steel Zinc Plate and Stainless Steel through our online store.
