A down-the-hole hammer drill bit assembly comprising: a drill bit having a forward cutting end and rearward anvil end, an internal passageway extending along a longitudinal axis of the assembly from the anvil end towards the cutting end; a foot valve seated partially within the passageway to extend axially from the anvil end; complementary abutment regions (304, 502) provided respectively at a radially inward facing surface of the passageway and a radially outward facing surface of the foot valve, the respective abutment regions (304, 502) configured to abut one another and axially lock the foot valve to the drill bit; characterised in that: the abutment regions (304, 502) comprise: a plurality of radially projecting lugs spaced apart in a circumferential direction around the axis; and a plurality of radially extending shoulders spaced apart in a circumferential direction around the axis; a circumferential separation distance between the shoulders is at least equal to or greater than a circumferential length of the lugs to allow the lugs to pass axially between the shoulders without substantially deforming the foot valve radially; an axially rearward end of each lug is tapered radially to provide an abutment contact surface and an axially forward end of each shoulder is tapered radially to provide an abutment contact surface; wherein a radial length of the lugs and shoulders are configured such that with the lugs positioned axially beyond the shoulders the abutment contact surfaces (402, 506) of the lugs and shoulders mate together to overlap radially within the passageway and provide friction fit regions that axially lock and inhibit independent rotation of the foot valve at the drill bit. a drill bit having a forward cutting end and rearward anvil end, an internal passageway extending along a longitudinal axis of the assembly from the anvil end towards the cutting end; a foot valve seated partially within the passageway to extend axially from the anvil end; complementary abutment regions (304, 502) provided respectively at a radially inward facing surface of the passageway and a radially outward facing surface of the foot valve, the respective abutment regions (304, 502) configured to abut one another and axially lock the foot valve to the drill bit; characterised in that: the abutment regions (304, 502) comprise: a plurality of radially projecting lugs spaced apart in a circumferential direction around the axis; and a plurality of radially extending shoulders spaced apart in a circumferential direction around the axis; a circumferential separation distance between the shoulders is at least equal to or greater than a circumferential length of the lugs to allow the lugs to pass axially between the shoulders without substantially deforming the foot valve radially; an axially rearward end of each lug is tapered radially to provide an abutment contact surface and an axially forward end of each shoulder is tapered radially to provide an abutment contact surface; wherein a radial length of the lugs and shoulders are configured such that with the lugs positioned axially beyond the shoulders the abutment contact surfaces (402, 506) of the lugs and shoulders mate together to overlap radially within the passageway and provide friction fit regions that axially lock and inhibit independent rotation of the foot valve at the drill bit. the abutment regions (304, 502) comprise: a plurality of radially projecting lugs spaced apart in a circumferential direction around the axis; and a plurality of radially extending shoulders spaced apart in a circumferential direction around the axis; a circumferential separation distance between the shoulders is at least equal to or greater than a circumferential length of the lugs to allow the lugs to pass axially between the shoulders without substantially deforming the foot valve radially; an axially rearward end of each lug is tapered radially to provide an abutment contact surface and an axially forward end of each shoulder is tapered radially to provide an abutment contact surface; wherein a radial length of the lugs and shoulders are configured such that with the lugs positioned axially beyond the shoulders the abutment contact surfaces (402, 506) of the lugs and shoulders mate together to overlap radially within the passageway and provide friction fit regions that axially lock and inhibit independent rotation of the foot valve at the drill bit. a plurality of radially projecting lugs spaced apart in a circumferential direction around the axis; and a plurality of radially extending shoulders spaced apart in a circumferential direction around the axis; a circumferential separation distance between the shoulders is at least equal to or greater than a circumferential length of the lugs to allow the lugs to pass axially between the shoulders without substantially deforming the foot valve radially; an axially rearward end of each lug is tapered radially to provide an abutment contact surface and an axially forward end of each shoulder is tapered radially to provide an abutment contact surface; wherein a radial length of the lugs and shoulders are configured such that with the lugs positioned axially beyond the shoulders the abutment contact surfaces (402, 506) of the lugs and shoulders mate together to overlap radially within the passageway and provide friction fit regions that axially lock and inhibit independent rotation of the foot valve at the drill bit.