screw stone

A popular name for the cast of a fo il encrinite. [FOSSIL-SCREW, 8. ] screw-tap, subst. An instrument for cutting the interior thread on a hollow screw. [SCREW-PLATE.] screw-tree, s. Bot.: The genus Helicteres (q. v.). screw-valve, s. A faucet or stop-cock actuated by a screw. [STOP-VALVE.] screw-well, 8. Ship build .: A hollow in the stern of a ve el into which a propeller is lifted.