A disc brake comprising: an actuation mechanism; a disc brake rotor arranged to rotate about an axis; first and second brake pad mounting structures (60, 61) to be located, in use, adjacent opposing inboard and outboard faces respectively of a brake rotor to be braked; first and second brake pads located by the first and second mounting structures (60, 61) respectively such that upon application of the actuation mechanism the pads clamp the rotor and brake torque is reacted by the pad mounting structure; wherein to prevent or inhibit fitting of the first and second pads, individually or in combination with friction material facing away from the rotor the first and second mounting structures (60, 61) comprise first and second formations (68, 70) on radially inner faces thereof, which first and second formations (68, 70) extend radially outwards therefrom and do not have mirror symmetry about a plane defined by the centre of the rotor, radial axis R and a circumferential direction C normal to both rotational axis A-A and axis R; characterised in that: the formations (68, 70) are remote from abutment surfaces (62, 63) for supporting the first and second pad in a radial direction, and wherein a spacing axially between the rotor when in a fully worn condition, and formations (68, 70) is such that a fully worn pad having a complementary formation therein is only capable of being successfully fitted in with its remaining friction material facing the rotor. an actuation mechanism; a disc brake rotor arranged to rotate about an axis; first and second brake pad mounting structures (60, 61) to be located, in use, adjacent opposing inboard and outboard faces respectively of a brake rotor to be braked; first and second brake pads located by the first and second mounting structures (60, 61) respectively such that upon application of the actuation mechanism the pads clamp the rotor and brake torque is reacted by the pad mounting structure; wherein to prevent or inhibit fitting of the first and second pads, individually or in combination with friction material facing away from the rotor the first and second mounting structures (60, 61) comprise first and second formations (68, 70) on radially inner faces thereof, which first and second formations (68, 70) extend radially outwards therefrom and do not have mirror symmetry about a plane defined by the centre of the rotor, radial axis R and a circumferential direction C normal to both rotational axis A-A and axis R; characterised in that: the formations (68, 70) are remote from abutment surfaces (62, 63) for supporting the first and second pad in a radial direction, and wherein a spacing axially between the rotor when in a fully worn condition, and formations (68, 70) is such that a fully worn pad having a complementary formation therein is only capable of being successfully fitted in with its remaining friction material facing the rotor. the formations (68, 70) are remote from abutment surfaces (62, 63) for supporting the first and second pad in a radial direction, and wherein a spacing axially between the rotor when in a fully worn condition, and formations (68, 70) is such that a fully worn pad having a complementary formation therein is only capable of being successfully fitted in with its remaining friction material facing the rotor.