I have a project that asks for two lengths of pipe to telescope for length adjustment. I am looking for smaller pipe to slide inside larger pipe without excessive sloppiness. Total adjustments needs to be 2 feet from minimum to maximum, no less than 12" length of small pipe inside the larger pipe.

Choices are
A: 2-1/2" inside 3" or
B: 3" inside 3-1/2".

Specs for sch 40 pipe of those sizes (from Engineeringtoolbox.com)

Nominal OD ID
2-1/2" 2.875 2.47
3" 3.5 3.07
3-1/2 4.0 3.55

A: If I try to slide the 2-1/2" pipe inside 3" pipe the spec shows 0.195 clearance (0.0975 all the way around) which looks like plenty of room, almost a sloppy fit.

B: If I try to slide the 3" inside 3-1/2" pipe the spec shows 0.050 clearance (0.025 all the way around) which looks almost snug. But what of the root bead from the welded seam during manufacture? Regrettably I do not have much opportunity to view or test fit before making a purchase.

Any suggestions?

- Mondo