The web-locker retractor has a pair of identical clamping wedges having teeth which are shaped to penetrate the material of a seat belt in order to displace the fibres of the material and engage therewith. Upon an engagement with the belt, the teeth interfit with those of one wedge fitting between those of the other. The teeth are arranged in arrays one of which is an offset mirror image of the other. The teeth of the two arrays are inclined oppositely to the direction of belt protection. Posts and sockets on the wedges co-operate to restrain the wedges to move perpendicularly to the belt plane, against a biasing spring. Upon locking, the web locker does not deflect the belt and therefore does not have to overcome a component of the tensile load on the belt. A retractor of light construction is therefore possible.