Abstract: A releasable locking device comprising a first and a second member movable into and out of engagement with each other, and one or more latch elements arranged within an inner space defined by said members when engaged. The latch elements are freely movable in that space which includes an annular channel, under the influence of gravity between a first position in which they do not interfere with movement of said members into and out of engagement with each other, and a second position in which the latch element or elements block movement of said members out of engagement with each other. The said members preferably comprise a socket member having a recess and a tubular stud member receivable therein. Due to the fact that the latch elements are movable under the influence of gravity the position or orientation of the locking device determines whether the latch elements are in their locking or releasing position.