For years the standard warning was always use black pipe, galvanized isn't consistant, flakes,etc. Gary Rogowski wrote in Fine Woodworking mag. that he has used galv. pipe for over 30yrs with no problems. I know atleast two other woodworkers that use galv. I don't have any pipe clamps,but when i did use them i don't remember any issues with either kind. my advise would be use what ever pipe you want to.
regards
jerry |