The bolts are 3/8" course thread. Look at the replacement starter and you can see what length the bolts would have to be - thru starter plus half inch minimum (maybe 3/4"). The starter bolts had a knurled shaft. If you want I have spares, send me the starter thru dimensions and I will send you the bolts. My e-mail is rscotm@cox.net, include your address. Due to shipping send my $5 when you get the bolts or buy my a drink at GN2017 - I will need it.