850 Lock Ring

Short are for the balanced pipe setup, the spherical seats and other parts are thicker than the earlier simpler setup so the nut thread can be shorter. But the best material for these nuts is bronze so I use long bronze ones as the expansion rate is closer to aluminium, once on the bike you do not notice. The factory only had 2 types of pipe, unbalanced with flat ends and balanced with conical ends which go with the spherical seats. With the issues with balanced pipes fracturing the aftermarket pipes dropped the balanced pipes but kept the conical seat hence the various types. In practice if you keep the spherical seats both types of pipe fit and the spherical seat allows the pipe angle to be adjusted which helps keeping the kickstart clearance, downside is less threads in the head are used but if the nuts do not come loose that's not an issue.

With all these various permatitions of pipes available just make sure you get ones with the MK3 shape, the primary case is bigger on the MK3 so especially on that side it must be MK3 or you will have clearance issues. I have a MK2A so have more choices but even for pre MK3, balanced pipes are thin on the ground and good ones even less.