THIS FITS OVER A SQUARE SHAFT ABOUT 1/2" BY 1/2" 3 1/4" LONG THIS IS ONE OF 2 OR 3 DIFFERENT PART NUMBERS THAT HONDA SAYS WILL FIT ON THIS SQUARE PEG , BUT THIS IS CORRECT LOOKING FOR THE ST90, BUT I AM GOING TO GET THE OTHER NUMBERS TO SEE IF THERE IS A BETTER MATCH FOR THE Z50'S K3 AND K4'S (SEE_OUR_220W) Honda MT250 1974, 1976 Honda MT250K1 1975 Honda SL100 1970 Honda SL100K1 1971 Honda SL100K2 1972 Honda SL100K3 1973 Honda SL125K1 1972 Honda SL125K2 1973 Honda SL70 1971 Honda SL70K1 1973 Honda ST90 1973 Honda ST90K1 1974 Honda ST90K2 1975 Honda XL70 1974, 1976 Honda XL70K1 1975 Honda Z50AK3 1972 Honda Z50AK4 1973 59K 59K ID = 16MM SQ.