Okay, after an extensive search here and on the net... I have decided to pose this question to my fellow HAMBers. In regard to lake pipes and lake pipe caps. The range of pipe diameters range from 1.5 to 2 inches on commercially available pipes. This range seems to affect the size of flange hole (obviously) and the center to center bolt measurement used for the caps. There doesn't seem to be a standard as far as the flange measurements are concerned. So my question is... what is the most popular pipe size? I am trying to make custom caps and I am really torn on what size pipes to accommodate. Or do most who have lake pipes make or have them made? Engines and exhausts are not my thing so any help would be greatly appreciated.