How to Insert a Cotter Pin

Written by dale yalanovsky
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Cotter pins, or cottar keys as they are sometimes referred to, come in all shapes and sizes. They are primarily used to secure a nonstress-related joint where two parts need to be held together, to secure screws, nuts, and bolts after they have been screwed in and to secure clevis pins that hold working parts together. Since a cottar pin will be inserted into a hole, always use the largest possible diameter that will fit.

Skill level:
Moderately Easy

Things you need

  • Framing hammer
  • Pliers
  • Wooden mallet

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  1. 1

    Position the end with the prongs of the cottar pin at the insertion hole entrance. Position the axis of the eye on the cottar pin parallel to the shank when securing a clevis pin.

  2. 2

    Gently tap the cottar pin into the hole with your hammer. Seat it all the way into the insertion hole until the cottar pin head rests firmly at the entrance.

  3. 3

    Spread the cottar pin prongs open with the pliers by grasping each one and pulling it apart and away. You want to pull and separate them enough to mimic the way a cheerleader does the splits with their legs.

  4. 4

    Tap each prong with a wooden mallet until both prongs have wrapped around the object they are securing and are as flat and flush as possible.

  5. 5

    Secure any nut or bolt that needs to be positively locked into place and remain stationary. Insert the cottar pin into the retention hole, then bend one prong over the top. Pound the prong down with the mallet as flush as possible, then bend the other prong downwards, also pounding it down as flush as possible.

Tips and warnings

  • For safety sake and holding power, never reuse a cottar pin, always put in a new one. Never bend a prong over the diameter of the bolt that needs to be secured. If there is no recourse, cut the prong to conform to this rule. Never bend a cottar pin prong to rest against a washer. Cut the prong if needed to make sure this does not occur.

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