I'm sorry if I appear really stupid asking this question, I've tried googling but got no luck. I know there are loads of variations of shermans built, different marks, large/small hatches, high/low bustle etc and to be honest I've never really gotten to grips with all of them.

The thing that really puzzles me though is why did some shermans have the curved cast hull front grafted onto the welded angled type of hull? I believe they were called composit or hybrid shermans.

Sorry again if I appear totally thick but it does seem a strange way to build them.

I think you are referring to the Composite Hulled M4 which was done as the Last of the M4’s it was believed by the US Army that Cast material was more resistant to penetration than the Rolled Steel plate. So for the last batch of M4’s they had a Cast Front welded to the Rolled Steel sides and top.
HTH
Jeff Larkin

Thanks for the info Jeff, much appreciated.