I need to order a new set of wheel cylinders, but I need to determine if my rear brakes are 9" or 10".

I have a 1999 3.0 V6 with 4x4, auto tranny. 4:10 gears, rear factory drums, open diff.

I assume just measure the inner diameter of the drum?

 

Look here: https://www.ranger-forums.com/drivet...m-size-135609/

9" have ribbed drums
10" are smooth drums

 

Perfect, thank you Ron.