a lockable shopping cart wheel comprises a plastics hollow casing , an axle on which the casing is rotatably mounted and a resetable locking mechanism that is mounted on the axle in the casing . the casing has an end wall , a cylindrical wall having a tyre and an end wall . the locking mechanism includes a locking plate which is axially displaceable but rotationally fixed to the axle . a coil spring acts between wall and plate urging it towards wall . the plate defines formations which can engage the wall thereby locking the wheel . between the plate and wall are three gear wheels , and which meter the number of revolutions of the casing and release the plate when a predetermined number of revolutions has taken place . the plate is ferromagnetic , allowing the plate to be displaced against the spring action to reset the locking mechanism by using a magnet from outside the casing .