So I have joined two parts together into one using the Join function and put them into my main assembly, but now it says 'surface bodies' next to the model and not 'part'. It also looks a bit dodgy in the assembly.

I have read a few posts on surface bodies about thickening or knitting etc but I am confused. I don't have two surfaces to knit together because as far as I can see it is one part, and I'm not keen on thickening it because it is a gear with very fine tolerances.

I have attached my file if anyone is able to have a look at if for me.

Cheers,

Jacob