This is the chart I use for selecting the best disc brake rotor for a conversion. This is a considerable improvement over wandering around a junk yard with a tape measure!
Rotor od = outside diameter of the rotor
Hub hole dia. = size of large center hole that the hub sticks through.
BS thickness = thickness of the rotor itself where the pads fit over it.
Overall HT = Total hight if you layed the rotor on a table and measured from the table to the highest point on the rotor.
No. Holes = number of wheel lugs.
Dia. = wheel lug pattern diameter.
Remarks = Solid or vented type rotor.
The following 10 page chart lists 580 of the most commonly used disc brake rotors by O.D. starting at 8" diameter and going to 15".
The column to the left has the Aimco part number so that once you know which rotor is usable for your project you can look it up in an Aimco part book and find which vehicles it was used on.