bottle screw

With each lurch of the vessel to starboard the bottle screw strained, until the young officer felt certain that the last two threads had stripped and the last restraining bonds had been loosed.

The chain that secured it to its fellows had at one time been set up by a massive bottle screw.

Possibly the thread was an easy one, but, in any case, the constant working of the ship had caused the bottle screw to "run back".