136094 ⎘
Props ; Chocks, e.g. made of flexible containers filled with backfilling material; Telescopic props with parts held together by positive means, with or without relative sliding movement when the prop is subject to excessive pressure with axial screw-and-nut, rack-and-worm, or like mechanism with screw, worm, or the like, not self-locking but normally prevented from rotation by friction members which slip upon excessive pressure