MRBF confustion

[geoffr]

I have been thinking about using a couple of MRBF fuses, but I'm not so sure now. It seems that the MRBF from Blue Sea (and their supplier) only come with a M10 - 3/8" battery connection and a 5/16" stud:

https://www.bluesea.com/products/519...k_-_30_to_300A

All of my batteries have 5/16" Studs (Engine,House,Thruster) which seems the most common.. so why on earth would they have a 3/8" battery connection?

Also why would they have different battery and stud connection sizes?

(yes the 5/16" battery stud would work on the 3/8", but it seems odd).