Shimano Hollowtech 2 crankarm bolt 20mm made for MTB Octalink bolts include steel washers、 JIS includes black plastic caps HT2 mount bolts (low torque plastic、 except XTR-M970 aluminum) are for mounting non-drive arm Hollow bolts not recommended for non-treated spindles SH-21102 SH-21502 have 8mm hex and SH-21504 has 11mm hex