Hey you know that attena you got? I got this one and it seems to be the same one you have.

Black Carbon Fiber Short Stubby Billet 3" inch Antenna | eBay

Anyways it came with 3 different sizes of screws and 2 washers. The problem is I tried all of them and even with the washers there is such a gap so you can still see the gold screws after tightening.

Yours looks so clean....