Cotter Pins

Cotter pins are wire-formed fasteners used by maintenance and assembly teams to retain two parts of a mechanism or secure components in holed applications. These pins support commercial assembly, service, and repair work with looped-head, split-pin, and self-locking designs that fasten externally accessible connections.

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Helpful Buying Guide

Cotter Pin Buying Guide

Choose cotter pins by matching the listed size to the assembly requirement, then compare the pin design, material or finish, and pack quantity needed for the job. The available selections include metric and inch sizes, looped-head designs for mechanism connections, and self-locking styles with prongs for holed applications.

Visual Guide

Popular examples in this category

M2.5 x 25 mm Steel Zinc Cotter Pins, 100-PackM2.5 x 25 mm Steel Zinc Cotter Pins, 100-PackWBB2291424M4 x 50 mm Zinc-Plated Steel Cotter Pins, 100-PackM4 x 50 mm Zinc-Plated Steel Cotter Pins, 100-PackWBB2291405316 Stainless Steel Cotter Pins, 1/8 in. x 1-1/2 in., 100-Pack316 Stainless Steel Cotter Pins, 1/8 in. x 1-1/2 in., 100-PackWBB2252133Carbon Steel Zinc Clear Cotter Pins, 1/8 in. x 2 in., 250 per PackCarbon Steel Zinc Clear Cotter Pins, 1/8 in. x 2 in., 250 per PackWBB2251103
Use Cases

Retain parts in mechanical assemblies

Cotter pins are used to fasten two parts of a mechanism together or to secure components through accessible holes during maintenance and assembly work.

How to Choose

Match size, design, and quantity

Compare the stated metric or inch size, select a looped-head or self-locking design based on the connection, and choose a pack count that fits stocking or repeat-use needs.

Applications

Support holed and external connections

Self-locking cotter pins are suited to externally accessible holed applications, where separated prongs help hold the connection in place.

Additional Information

Compare construction details

Available details include steel, 316 stainless steel, carbon steel, zinc or clear zinc finishes, extended prongs, square-cut prongs, double-bodied pins, and half-round wire construction.

M1.6–M4Metric sizes listed

Metric cotter pins are available from M1.6 x 10 mm through M4 x 50 mm.

1/8–5/16 in.Inch diameters listed

Inch-size selections begin at 1/8 in. and extend to 5/16 in. diameter.

25–250Pieces per listed pack

Pack counts shown range from 25 pieces to 250 pieces.

3Material types listed

Selections include steel, 316 stainless steel, and carbon steel.

Comparison Guide

Compare Cotter Pin Types

Use this overview to compare the product styles represented in the category.

Product typeListed characteristicsPack options shown
Looped-head steel pinsDouble-bodied or split-pin designs for fastening two mechanism parts; looped head100 pieces
316 stainless steel self-locking pinsSelf-locking design with extended and square-cut prongs for holed applications50 or 100 pieces
Carbon steel self-locking pinsSelf-locking design with extended and square-cut prongs; zinc, clear zinc, or yellow zinc finishes are listed on select options25, 50, 100, or 250 pieces
Planning Guide

Plan the right fit before choosing

Start with fit

Match the pin to the stated assembly size

The range includes metric sizes such as M1.6 x 10 mm, M2 x 20 mm, M2.5 x 25 mm, M3.2 x 40 mm, and M4 x 50 mm. Inch-size options include 1/8 in. x 1 in., 1/8 in. x 1-1/2 in., 1/8 in. x 2 in., 3/16 in. x 1-1/2 in., 3/16 in. x 2-1/4 in., 1/4 in. x 4-1/2 in., and 5/16 in. x 4-1/2 in.

  • Use the listed dimensions to match mechanism or holed-assembly requirements.
  • Compare metric and inch measurements carefully.
  • Select the length shown for the connection being fastened.
Compare pin styles

Choose a design suited to the connection

Looped-head, double-bodied, and split-pin options are intended for fastening two mechanism parts. Self-locking wire-formed options install through a hole, and their extended prongs can be separated to help retain the assembly.

  • Looped heads provide a defined head at one end.
  • Self-locking designs help secure components in holed applications.
  • Extended prongs help make separation easier during installation.
  • Square-cut prongs provide a cleaner finished appearance.
Plan your supply

Select material, finish, and pack count

Available constructions include steel, 316 stainless steel, and carbon steel. Listed finishes include zinc, clear zinc, and yellow zinc. Pack quantities range from 25 to 250 pieces, with many 100-piece options; one 250-count option has a 14-pack minimum order.

  • Choose from steel, 316 stainless steel, or carbon steel constructions.
  • Compare zinc, clear zinc, and yellow zinc finishes where listed.
  • Use 25-, 50-, 100-, or 250-piece quantities to plan stocking needs.
FAQ

Common questions before buying

What are cotter pins used for?

Cotter pins fasten two parts of a mechanism together or secure components in holed applications.

What cotter pin sizes are available?

The listed range includes metric sizes from M1.6 x 10 mm to M4 x 50 mm and inch sizes from 1/8 in. x 1 in. to 5/16 in. x 4-1/2 in.

What is the difference between looped-head and self-locking cotter pins?

Looped-head pins have a defined head and are listed for mechanism connections. Self-locking pins are wire-formed fasteners with prongs for holed applications.

Which pack quantities are offered?

Listed pack quantities include 25, 50, 100, and 250 pieces. The 250-count carbon steel zinc clear option has a 14-pack minimum order.

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