You must be referring to the difference between single pice and two pices discs/shafts. With two piece, the shaft runs through the disc and is pinned together with a screw. This allows for replacing disc and re-using shafts. Single piece, however, are safer for blow out prevention if no undercut is allowed in the shaft bores.
Hi joeswoes,
Thanks very much for your answer, yes pinned is with a screw to fix the disc on shaft, pinless is the shaft runs through disc, but what's different between them in advantage and disadvantage? Thanks.