Is it ok to use copper clamps on PEX pipe?
There is no problem chemically from using a copper clamp. However, that type of clamp is sharp enough that abrasion from pipe movement against the clamp from thermal expansion and contraction may over time wear a weak spot in the pex. There are plastic clamps specifically made for pex pipes.
Pex Install Guidelines
Check out page 13 for clamps. Plastic clamps are recommended but approved metal clamps are ok.
Thanks Paul and Brian