went to my local shop to get some new cleats the other day but the only shimano ones they had were the SH-52's for the 858. when i got home looked them up in the trade sales and support guide and it says there all right for my 636 pedals, but when i fitted them they had an annoying click on high power downstrokes. so i compared them with the old sh-51's and found that 52's have i little spike at the rear which the spring plate was sliding up and down as i pushed down and pulled up. Ground it off and ther nice and silent and not as hard to get out. Just a little tip for you folk out there