Akademik

an oblong metal ring with a spring clip; used in mountaineering to attach a rope to a piton or to connect two ropes

1. : a spring ring that is sprung open and snapped into place in its groove and is used especially for a piston or other retaining ring function

2. : an oval or pear-shaped ring used by rock climbers to fasten a rope to a piton

any of various kinds of metal rings that must be forced open to be used and snap back into place to make a snug fit.

[1900-05]

snap ring,

= piston ring. (Cf. ↑piston ring)