NOT MEASURING THE HEX END THIS IS 10MM DIA. X 5 1/8" LONG 57J @ *SELF_LOCKING 10MM SWING_ARM_NUT 50'S_70'S_90'S_110'S 90351-268-000 1/21M (207P) 207P @ *10mm_NUT_PLAIN 1.25_PITCH MANY_USES REAR_SWING_ARM BOLT CT70K0_&_HK0 94001-10000-0S 1/22M (65R)OEM HONDA 10MM NUT 1.25 PITCH THIS WAS STOCK ON SWING ARM BOLTS OF: CT70K0_&_HK0 65R @ 10MM LOCK WASHER KL 1/19K (10LOCK) 10LOCK @ *OEM_HONDA_WASHER 10MM 7/19M (B63H)OEM HONDA WASHER REAR SWING ARM/TOP & BOTTOM REAR SHOCK - 10MM FLAT WASHER (63H) B63H