Definition

Noun: A type of fastener or locking device consisting of a metal pin with a split at one end. After being inserted through a hole in aligned components (such as a nut and bolt), the two ends (prongs) are bent apart to secure it in place and prevent it from falling out. Its primary function is to prevent nuts, bolts, or other parts from loosening due to vibration.

Usage

A cotter pin is used to mechanically lock parts together. It is inserted and then its ends are separated (or "splayed") to lock it. It is a common, reusable fastener in mechanical assemblies. - It is typically used with a castle nut or a clevis pin. - The act of securing it is called "cottering."

Examples

• Securing a wheel:
• Safety mechanism:
• General use:

Advanced Usage

• Materials and Types: Cotter pins are commonly made of soft metals like mild steel, stainless steel, or brass. Variations include hairpin cotters (which have a looped end for easier removal) and standard split cotters.
• Engineering Context: In technical drawings and manuals, a cotter pin might be specified by its diameter and length (e.g., 3mm x 30mm cotter pin).

Variants and Related Words

• Split pin: A general synonym for a cotter pin.
• Cotter (key): A related but different fastener; a tapered wedge or key driven into a slot to secure a part, often used in older machinery (e.g., a cotter joint).
• Clevis pin: A type of pin that is often secured a cotter pin.

Synonyms

• Split pin
• Safety pin (in a mechanical/engineering context, not for clothing)

Related Phrases / Phrasal Verbs

(Not typically applicable for this noun)

Related Idioms

(Not typically applicable for this noun)

Noun

1. a cotter consisting of a split pin that is secured (after passing through a hole) by splitting the ends apart