Percussion drill bit

A percussion drill bit having an anvil portion and a head portion, with connecting means therebetween to transmit torsional and percussive axial forces from said anvil portion to said head portion, a plurality of cutting inserts arranged on the cutting end of said head portion in a pluraliity of circumferentially-spaced groups, said cutting end having fluid flow passages thereacross separating said groups of inserts, at least some of said inserts being so arranged that during drilling operations said some of said inserts penetrate the formation being drilled by generally equal amounts and are thus subject to generally the same loading, corresponding sets of inserts, one set from each group, being at the same radial distance from the drill axis, and successive inserts in one set, in the direction of rotation of the drill, being at progressively lesser axial distances from a reference plane transverse to the axis at the lowermost end of the head portion, and at the same axial distance from said reference plane as corresponding inserts in the other sets, the spacing between inserts in each set being substantially uniform, and the outermost of any radially adjacent pair of sets having a greater number of inserts than the innermost of said pair.