U Clip Woes

This is what they are.

http://www.grainger.com/Grainger/UNut-4CUG6

The problem is to keep consistent with the bolts I need to use the same thread and bolt size otherwise I will have different size bolts and I dont want to do that if at all possible. Pluse the spacing available under the front cowl is very small so a larger bolt would be VERY difficult to get into there.