I replaced mine just this summer. I purchased new sheaves from Schaefer with 5/16" bores(I'll find the part number if you're interested), and drilled out the rivet in the old block. (The rivets seem to be pretty hard, use a lot of oil.) Then, I bored out one side of the rivet hole in the bracket to accept a 5/16 dia. stainless shoulder bolt (1/4-20 thrd on the end). I left the hole in the other side of the bracket small as clearance for a 1/4 thread. I fed the shoulder bolt thru the 5/16 clearance hole, thru the sheave, and let the 1/4-20 end of the shoulder bolt protrude thru the opposite bracket. Then I put a jam nut on the shoulder screw, locking it to the one side of the bracket. Then you can trim off the head of the shoulder bolt. I did it this way instead of just putting and pin and cotter keys in it so that I knew the sheave was spinning on the shoulder bolt and the shoulder bolt wasn't spinning relative to the bracket. I sailed it hard in Florida all last week and it works great so far. I'll post a pic later.