Hey, I was going to try to take off my heater blower to oil it up on my 72 Dart with a/c, but I found out it would not come out at the firewall like I was thinking, two isolation mounts did not come out, but one was all ready loose like somebody has mess with it before, So I went to put it back & the one that come out broke off when I went to put it back & I just snuged it down not much at all!... So what size of isolation mount for the heater blower do I need to get for my 72 Dart?

I've seen em at mc master carr. What size thread are the studs?
Looks exactly like the ones I got from them for the motor on my old valve grinder
They we're but about $4-5 each

I,m not the best with a tape measure, so I just want to know I order the right one on stud size & stuff!

it "looks like" a 3/8-16 thread size from the picture. [provided my "calibrated eyeball" was zeroed out correctly. ]
however, before ordering one, take a look at what your local hardware or building supply store has to offer.
my local ACE hardware stocks those isolators in various sizes, and the ACE hardware in the next town over has almost three times as many different items stocked for industrial and automotive use.

While there, you can establish the thread size, I'm guessing 5/16 x 18