As above, they are to set the end float of the selector shaft. I didn't require them in mine, nor were any removed before I fitted the new bushes (but the old bushes were heavily worn!). Simply put, you really want as little end float as you can get away with without it binding up when hot or even when the inner cover is tightened - with little to no end float all the motion imparted by the cams is used to move the forks and the selector dogs rather than moving the selector shaft. The excess endfloat on my selector shaft, coupled with a worn fork and groove caused 3rd gear to drop in and out of mesh - it's worth getting right!