HANSON RIVET S25MG280 Steel PRE-BULBED Shank, Multi-Grip Rivet-NUT Gold ZINC Finish, 1/4-20 X .020-.280 Grip Range (Pack of 25)

Would these do well on galvanized pipes that are round vs square?

Who makes a mandrel for this? Drill/Impact and bolt not working in particular application.

What size drill bit is suitable for installing these? I'll be increasing the size of various existing holes in my Sprinter van to fit these. Thanks

Is there a 1/4-20 that is shorter than 1"? (Don't have enough clearance on back, but need the strength of 1/4")?