Help, Axle caps

Lost my Ford racing logo axle cap last night on the way to my dads house and just want to know if those are supposed to be loose because both sides were loose. I had my new Prostar wheels without the center caps on so you can see the Ford racing logo. The right side tightend up some how, I guess centrifical force tightened it up. I'm pretty sure by looking at the axle the caps have a stud on them. Maybe they are supposed to have thread locker on them. Any help would be greatly appreciated.

Ok, no one replied so I'll try it again. Anyone with Ford racing axles should know what I'm talking about. I went ahead and took the one that is on the right axle off and found out it screws out but the stud on the cap is not fixed so I'm not sure how hard it will to screw back on. Anyway new question, this cap has some weight to it, 4/8 ounces does it have a reason other than looks or is it for balancing purposes? Also, with my BFG drags at the track I had a shimmy or a out of balance feel above 90 mph, is this normal with drag radials set at a low pressure [14psi]?