A curled variable radius lever comprises a lever arm 2 of variable effective length that curls and uncurls about a drive axis. In a preferred arrangement the lever assembly has a plurality of rigid blocks 3 articulated together by a chain 4 with link pivots 5 which are affixed to respective blocks 3. Each block 3 has a pair of facing walls 11 and a pair of facing mutually inclined sloping walls 12 which abut when the lever arm 2 is in a curled condition. The lever arm 2 is pulled into the curled condition by a coiled tension spring 13 and restrained in this position by a magnet 9. When it is uncurled the walls 11 abut. The chain 4 then prevents the arm 2 from bending further when a driving force is applied by users to a handle 6. The lever may be used with socket sets, yacht winch, fishing rod reel, a bicycle crank or a jack assembly.