[BHerring]

Afternoon all,
I have a 1993 D250 and I need to replace the rear wheel cylinders. When I search on Napa for the parts I need to know the brake dimensions like:

11" X 2 1/2 " brakes or
12" X 2 /2" with 1" Bore

What I need to know is what am I suppose to measeure: brake shoes? and I have no idea what the bore is?

Any information will be greatly appreciated.

Thanks