Abstract: A support structure for a castor, a castor provided with such a support-structure, and a castored trolley is described. The support structure comprises a first member 5, a second member 3 that is rotatable with respect to the first member about a pivot axis, and magnetic means 21, 23, 61, 63 that is operable up to a certain torque to restrain movement of the rotatable member from one angular position with respect to the first member. Preferably the magnetic means comprises at least one hair of magnetically co-operable components. Preferably one component of the at least one pair of components is a permanent magnet. In another angular positions without registration of the first and second members free rotation is possible unless and until re-registration occurs.