I'm constructing a garbage (shopping) bag holder/dispenser consisting
of about 28 inches of 7 inch metal duct pipe, a cap (also duct and
this is actually on the bottom), a webbing strap to attach it to the
wood above the space next to the refrigerator, and vinyl similar to
seat covering to cover the piping and the hand hole in the side.

I was attaching the cap to the bottom with pop rivets but
unfortunately I broke the gun so I'm in the market for a new one. In
reviewing the available options I see that there are ones with 14 and
18 inch handles. Great idea. I'm as weak as a kitten and extra
leverage would help a lot. But...

All this opens up a can of worms. Should the blind side of the rivet
be the same shape as the visible side (i.e. a barely discernible bump)
or should 90% of the blind rivet be still un-flattened? The current
situation is mostly un-flattened but if this is the correct state of
affairs these have to be cut off so they don't tear the bags.

The web is annoyingly simplistic in all the how to's on the subject. I
have yet to find one that describes:

When to use aluminum and when to use steel.

Which # is first (or second). Is the first number the diameter of the
hole I need to drill and the second the thickness of the plate to be
joined? In which case I should be looking at a 1/8 by (18 + 18ga) but
such a rivet doesn't exist. Supply exists of things like 1/8 * 3/8
inches. Yikes! That implies two plates totaling 3/8 inch thick. A
massive piece of steel! Obviously I'm reading this all wrong.

What size and type of gun do the people who use these frequently (not
in a factory environment) choose?