bitt pin

listen to the pronunciation of bitt pin
Английский Язык - Английский Язык
a pin through the bitthead to keep the mooring lines from slipping off
Similar to a belaying pin but of heavier scantlings; a turned length of wood or metal passed through the bitts or cross-piece, used to prevent the cable from slipping off or over the bitt-heads yet removable so as to facilitate doing so