Mark, all 10 speed chains are not the same pin width. Shimanos HGX’s are 5.8, conex are 5.9 and kmc and others are 6.2. so I guess that may not all work on shimano 10 speed blocks. I may be wrong. You can buy 9 speed 12:39 blocks and I’ve looked at my mechs and recon they will clear. I’m going to run 1 x 10 so I want as bigger rear block as poss.