Most of the Mac air drills going back many many years are rebranded IR drills.
Solid product with the standard 'tool truck" and "MAC brand" markup.
Used air tools are a **** shoot. Not a lot of ways to tell wear and usage and if not oiled or cared for, they are a poor tool investment.
Caveot emptor totally applies.
I personally only buy used air tools from friends, coworkers or rebuilt off the truck.
It's just too big a risk unless the price is so low you cannot pass and have the money to gamble and lose.
