Abstract: A vehicle immobilization device comprises a pair of chocks (1 and 2) for abutting a vehicle wheel on either side (in a direction of rotation) of its ground contact point, a top hook (7) for hooking over the wheel at a point over the ground contact point, a chock arm (3, 4) secured to each chock, the chock arms being relatively movable to adjust the separation of the chocks, and an adjustable length stem (5) for connecting the top hook to the chock arms and including a lock (6) to arms (3 and 4) include oppositely facing channels (9 and 10) with complementary corrugated strips (41 and 42) which are interengageable to prevent relative movement of the chock arms at one of a plurality of positions in which the stem can be locked to the chock arms, by movement normal to the direction of chock separation adjustment.