to the disc additional slots such as slot 302 shown in fig2 or other surface features may be added in order that the retainers will break at defined locations during disassembly thus when the retainer is pried on to remove the knife the section of the retainer that is engaged with the tabs or projections of the knife adapter or disc will separate from that portion that is engaged with the pin this would allow both of the resulting pieces to be easily removed 0054 fig1 and 20 illustrate optional configurations of the grooves in the pin 140 and 240 the grooves could be full annular grooves 247 as illustrated in fig1 or slots 245 one on each side as illustrated in fig2 0055 fig2 and 23 illustrate an additional embodiment of a retainer 350 with an additional curved section 352 the end 354 is narrow enough to fit into the key hole slot of the retainer similarly shaped to the key hole slots in retainers 130 and 230 the end 354 will then engage with the groove in the pin to increase the bearing surface under the pin head and providing a locking feature that prevents the retainer 350 from sliding end section 356 forms a tapered profile approximately paralleling the raised portion 128 228 of disc 120 220 such that the disc 120 220 will protect it obviously many modifications and variations of the present invention are possible in light of the above teachings including variations in the shape of the knife mount pin and cooperating apertures in the knife adapter it is known to use various configurations.