Interesting. I use Jconcepts wheels, which I think are thinner. They used to make half height nylocks, which would also work.

I bought the Proline front end because I was in a hurry (I wanted to race this weekend, and it's a brand new to me truck, since I didn't have any tires I wanted to use the same tires I have for my SC4x4) and I figured WTH? Mine has no slop. The PL aluminum hexes are the same size as the Jconcepts ones.

Maybe I got lucky.