Definition
A circular spring-steel retaining ring that fits into a machined groove on a shaft (external snap ring) or inside a bore (internal snap ring) to hold a part in position. The ring is compressed or expanded with snap-ring pliers to install or remove it, then springs back into the groove to lock the assembly together.
Plain English
A small, springy metal ring that drops into a groove and keeps a part from sliding off a shaft or out of a hole. It pops in and out with special pliers.
Context Anchor
Seen in aircraft maintenance when inspecting or assembling parts that must stay fixed on a shaft or inside a housing.
Derivation
Called a 'snap' ring because it literally snaps into and out of its groove when released by the installer's pliers. The action of springing back to its original shape is the defining feature.
Why Pilots Care
Prevents critical rotating parts from moving out of position, avoiding engine or control-system failures.
Intuition Check
Do not think of a snap ring as just a washer or spacer. Its job is to lock into a groove and retain another part in position.
Example Sentence 1
The mechanic used snap-ring pliers to remove the external snap ring before pulling the bearing off the shaft.
Example Sentence 2
During the cylinder inspection, the mechanic checked that the snap ring was fully seated in its groove.