I know an old cwi that told me about the templates a few months ago, asked me what thickness it was for and I said....."uhhh, the right one??" and he told me that different thickness of pipe will make a difference. I never really thought about it until he said something and when I drove home I ran it around in my pea brain and said, "oh yeah"(lightbulb moment). Different thickness equals larger o.d etc, layout changes.

I have found the "store bought" templates to be good for small pipe under 4" in general fabrication where a perfect fit is not needed. For me anything that I want a perfect fit on I make my own template out if brass shim stock. Lay out my fit with the blue book, grind for the perfect fit then use that piece to make my template with. Aluminum flashing you buy in a roll at the hardware store works decent also if you cant find brass shim stock. In my experience "round" pipe is a relative term, especially with large and or thinner wall thickness. This adds much headache to achieving that perfect fit. I use brass shim stock for templates on many different kinds of steel not just pipe. I have a huge assortment just for I and H beams. Works good for me.