How to identify Rim size/ make ?

Have a look on the inner side of the rim as in the side away from the road and clean around the rim and you should see a set of numbers stamped into the metal
Like

J 16 x8 JJ TOPY 1008 03 58.0

Similar to that which is a 100 series rim

Just as a help PCD (pitch circle diameter) is not the distance from one stud center to another. It is the diameter of the circle that all the studs are on with the center of the circle being the center of the wheel.

Holdens are about 102mm, Ford Falcon are 114.3mm, F100 138mm.

You will also need to consider the center hole diameter, eg early Falcon (pre 1972) is smaller than later falcon and while you can fit a late model wheel on an earlier model you can't do the opposite.

Based on the details here:

PCD Calculator

they are probably holden rims.

These are the most common trailer wheels as most come with these standard and you only get ford,toyota etc if you specify otherwise.

Cheers
Ross

Firstly, PCD stands for pitch circle diameter, which is an imaginary circle drawn through all 5 studs.

To work out your PCD, divide your 71mm by 0.58778 = 120.79mm.
This would suggest that your rims are Holden HQ to WB.
The trap here is that Commodore rims are similar....but not close enough to be interchangeable.

If you have access to vernier calipers, you can accurately measure across 2 of the studs and subtract the diameter of one stud, this will give you the correct spacing. For HQ to WB it should be 70.91 (120.65mm or 4.75" PCD), for Commodore it should be 70.53 (120mm or 4.724" PCD)

Hope this helps.

Cheers
Glenn