drum brakes

[Josh577]

Im looking to buy new wheel cylinders for the rear of my truck, online there asking me if i have 11” brakes or 13” brakes, is that the inside diameter of the drums?
my drums measure about 15 inches to the inside.
i looked around in here i did not see this question

 

[Blue Ox]

Inside diameter.

 

[justhorns]

Its the "diameter" of the brake pads when hooked in place (no drum), which contacts the drum. So, 13 x 2.5" brakes would also be 2.5 " wide pads

 

[Scott91370]

Drums can't be 15" to the inside. These trucks only came with 15" wheels.