A punch and die assembly for trimming the flared end of a can body comprises a reciprocable punch (10), and a split die (15) consisting of two semi-circular segments (14, 16) movable between an open position allowing infeed of article (A), and a closed position around the article. During co-operation of the cutting edges (35, 61) and (51, 62) on the punch (10) and die (15) respectively to trim the can body, the punch is centralized accurately in relation to the die by engagement of a radially outwardly facing surface (521, 74) on the die with a radially inwardly facing surface (321, 73) on the punch; rough alignment between punch and die having previously been achieved by engagement of further surfaces on the punch and die when the die was closed.