卸扣，索具的一种，是由扣体和销轴两个易拆零件装配成的组合件，广泛适用于电力、冶金、石油、机械、铁路、化工、港口、矿山、建筑等各行业。

根据扣体的形状主要可以分为D形卸扣和弓形卸扣。D形卸扣的扣顶呈半圆形，其内半径等于两环眼之间内宽的一半，也称U形卸扣或直型卸扣；弓形卸扣的扣顶呈大半个圆形，其内半径大于两环眼之间内宽的一半，也称Ω形卸扣或马蹄形卸扣。

A shackle, also known as a gyve, is a U-shaped piece of metal secured with a clevis pin or bolt across the opening, or a hinged metal loop secured with a quick-release locking pin mechanism. The term also applies to handcuffs and other similarly conceived restraint devices that function in a similar manner. Shackles are the primary connecting link in all manner of rigging systems, from boats and ships to industrial crane rigging, as they allow different rigging subsets to be connected or disconnected quickly. A shackle is also the similarly shaped piece of metal used with a locking mechanism in padlocks.