Hi Wolfman. As the novice that I am I had to go with what parts suppliers on the internet was telling me. They said there were two sizes of crackshaft oil seal and it was either, lets say 35 or 38mm. So I measured the crankshaft and then I measured the crankshaft collar and found it to be say 35mm. so I ordered the part believing it would fit. when I tried to fit it the inner fitted but the outer, which should have been 38 was infact only 37 and so blo.dy useless. I then found a Kubota dealer nearish me and phoned them up and ordered a front oil seal. They just said, yes still available, will take two days to come in and no question as to which size. So you are absolutley correct, there is only one size. Thanks Bernie