presser 37 for abutting contact with its closed end the open end of the clearance hole 40 is lipped or flanged at 41 to engage a stop 42 on the threaded rod 38 so that the rod is restrained from withdrawal out of the clearance hole fixedly mounted on the other end of the threaded rod 38 projecting out of the tapped hole 39 is a knob 43 which may be shaped like a wing nut as shown in fig5 thus by the manual turning of this knob 43 in either direction the presser 37 can be moved back and forth with respect to the set of trimming punches 30 carried by the floating punch holder 29 the presser 37 is recessed at 44 to accommodate projections 45 formed on that side of the workpiece 24 opposite to its upstanding walls 23 the punch die assembly 14 shown in fig1 c is further illustrated in fig2 as installed in its working position in the frame assembly 10 with reference therefore to both fig1 c and 2 the punch die assembly 14 has a die 46 fixedly mounted on a rectangular mounting plate 47 and a floating punch holder 48 carrying a perforating punch or.