Some one educate me on F1 boxes. Speedway sells an adapter that fits ford 32-48 that is tapered and keyed. I was researching the Grant adapters and saw they had one that fit 49-57 F series that is splined and another that fits 40-41 and 46-48 ford delux and 48 F series.This one is also keyed. I found another site that said splines were used on 39 and up trucks. My question is were there different splines on the earlier ones than the later ones or are they all the same . I'm not sre which adapter I need for my box. I was told it was a 48 F1 box but now I'm thinking it could be later. Mine has 39 splines with a 1/8 inch space on one side only. If they are splined from 39 and up , I'm confused on why the adapter for the Ford Delux and the 48 F series is tapered and keyed. Can anyone shed any light on this. I'm just trying to get a basic adapter for a 3 holed metalflake wheel on my F1 box.