When talking about Bmx rims?

Depending on the size of the rear driver you choose, you need to choose the coresponding front sprocket. ex 25t with 9t, 28t with 10t, 30t with 10t etc. 36 is the number of spokes, most people run this amount. 14mm means the size of the axel, a standard size if your looking for a freestlye wheel to go with a park frame. All race frames come with a 3/8 rear dropout so you will need a wheel with that size of an axel. you can run a 3/8 in a 14mm dropout, but you will need an adaptor.