Electrical Electric Fan Wiring Question

Hey guys,
I bought an electric fan kit from latemodelresto and it is missing the inline fuse holder.
I want to install the fan tomorrow so I went to the local parts store and got one.
Here's my question to you power gurus. I have a 10 gauge power wire and a 40 amp fuse but the only fuse holder I could find is rated for 30 amp and has 12 gauge leads. If I wire this in will I fry something?
I don't know crap about power so any assistance would be greatly appreciated.

Thanks

I decided to just wait and let latemodelresto send me the missing inline fuse holder.
If something were to go wrong at might void some sort of warranty if I substitute a part. Besides, I paid $350 for the fan kit and I shouldn't have to go by more parts to make it work. Thanks for talking some sense into me.