Reply by Gregn

I have both 1/2” and 3/4” black pipe clamps. For material 3/4” or less, and lengths of 36” or less I use the 1/2” pipe clamps. For these type of applications these work well without any problems.
For material over 3/4” and longer lengths I use the 3/4” pipe clamps. The 3/4” pipe clamps also allow you to add extensions for much longer lengths. I like to use the 3/4” pipe clamps for cabinetry and other such large items.

-- I don't make mistakes, I have great learning lessons, Greg