Mike, The original Chevy truck wheels have 6 but my 37 Buick has 3. I guess the generic answer is however many it takes to hold the hub cap on.
So, going a step further and reasoning some things out.....Generically speaking....1 clip per 10 miles an hour...the more the better and it all depends on how fast and what kind or roads you are going to be driving on. Now, you may be asking, ok, what about 60+ miles per hour? Who goes that fast? 50-55 is beautiful enough to speed thru life and enjoy the tap, tap, tap of the tappets. Oh, the answer to the 60+ part is then you go to a different counting system....it is called the silicone inch system! rod
Well, a bag of clips showed up from our host a few days ago, and I modified a wheel to accept 3 of them and installed an old hubcap. But... I think 6 is going to be the number. If I use Rod's logic, I'll need WAY TOO MANY clips.