what size compression fitting will fit over 1/2 copper pipe?
Plumbing sizes are standardized. So a 1/2 compression fitting for copper pipe will fit a 1/2 copper pipe. If it's for PVC, then it's designed for the dimension of a PVC pipe, etc. While John M is correct that plumbing is based on the inside dimension, if you match the same TYPE of fittings they will all work. Mixing fittings for different types of plastics won't work because they have different characteristics. Same for mixing copper and steel pipe. You can get adapters to change from one type to another. This is useful when doing a refit where the old pipe is steel and you want to install copper, or Pex (a flexible tubing type piping).
Plumbing sizes are standardized. So a 1/2 compression fitting for copper pipe will fit a 1/2 copper pipe. If it's for PVC, then it's designed for the dimension of a PVC pipe, etc. While John M is correct that plumbing is based on the inside dimension, if you match the same TYPE of fittings they will all work. Mixing fittings for different types of plastics won't work because they have different characteristics. Same for mixing copper and steel pipe. You can get adapters to change from one type to another. This is useful when doing a refit where the old pipe is steel and you want to install copper, or Pex (a flexible tubing type piping).
