Got another one for you guys !

[Bruce R]

Tried looking up the markings and got nowhere.

 

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[Charlie P. (NY)]

Looks like a rivet tool for "pop" rivets.

 

[releventchair]

It looks like a rivet gun.
Pli-grip is a modern metal strip for upholstery work.
Insul coustic might be the same co. that made/makes? firewall insulation for the auto industry. Mineral wool stuff early on.
Could the rivet looking tool have been how material was attached to firewall?
I don't know. (!)

 

[Bruce R]

I tried pop rivets in it, it dont grip them. Pop rivet tool was my first guess when I found it but it was pretty obvious that it’s something else. It’s very heavy, not a cheap p.o.s.

 

[releventchair]

It would likely have a pair of internal jaws to grip if it were for a rivet...
Worn or dirty ,misaligned jaws don't grip.
Anyways ,neat tool and no I still don't know what it is..

 

[nhbenz]

I think the description below is for your item, from this site: https://www.trademarkia.com/pligrip-72247887.html
[FONT=&quot]
TOOL EMPLOYED FOR FASTENING ALUMINUM JACKETING AROUND PIPE COVERING, TANKS, TOWERS AND OTHER EQUIPMENT REQUIRING JACKETING FOR PROTECTION[/FONT]

 

[Rookster]

It would likely have a pair of internal jaws to grip if it were for a rivet...
Worn or dirty ,misaligned jaws don't grip.
Anyways ,neat tool and no I still don't know what it is..

The different size mandrels are probably in a separate box.