I have a 1/2" diameter hole. I want to put a pipe inside the hole. What size PVC pipe fits into a 1/2" hole?

Did you guess 1/2" pipe? WRONG. "1/2 inch pipe" isn't half an inch big on the outside. It's closer to 7/8". You might think "ah so the 1/2" refers to the inner diameter". Wrong. The inner diameter of 1/2" PVC pipe is legally required to be 0.602 inches, according to the Schedule 40 standard. Want a pipe with outer diameter 1/2"? The closest size of PVC pipe is of course 1/4" PVC pipe. But even that won't quite work, because, 1/4" pipe has outer diameter 0.54", which is more than 0.5" and way more than the 0.25" in the name of the pipe. PIPE SIZES ARE ALL LIES

Guess how I found out? I'm building a telescope, and as part of that I'm building a mount. I bought a cheap collection of 3 pipes off the internet, but I needed a fourth, so I went to the hardware store to buy some pipe. Guess who learned a $6.99 lesson in nonsensical standards...