1300773 Trepanning tool E D HOUGEN 22 May 1970 [5 June 1969] 24854/70 Heading B3C A trepanning tool comprises teeth 26 Fig. 1, 2, each tooth having a downwardly projecting cutting edge 38, and an upwardly projecting cutting edge 40. Edge 38 has a front rake 28, Fig. 3, and edge 40, Fig. 4, has a front rake 30 whose angle b is smaller than the angle a of rake 28, and the teeth are formed on a thickened portion 18 of the wall 16 Fig. 2. Cutting edge 38 has a clearance c, Fig. 3, which is less than the clearance d of edge 40. The rakes may be positive, negative, or zero, so long as rake angle a is greater than rake angle b. The rake angle may progressively diminish in a radially outward direction. A gullet 48 Fig. 2 is provided so as to assist the removal of cuttings. In a modification, the teeth are arranged in three groups 26a, 26b, 26c, Fig. 8, or 26d, 26e, 26f, Fig. 8a, staggered in the radial direction. Gullet (70), Fig. 10 (not shown) is of different shape to gullet 48, Fig. 2. In a modification, the tool comprises a cylindrical blade 80, Figs. 13, 14, which is press fitted into a sheet metal cup 78, the blade 80 is not thickened at its lower end, and the cutting teeth 82a, 82b, are set radially inwardly and outwardly so as to provide clearance.