Hi sorry to answer late.
the original hole i think is 12mm when you remove the original bushing.You dont need to fill the hole.On the caliper now when you remove the bushing you make the bigger hole for align the caliper to the car.Now the thickness of the new busing is same as to cover the hole on the caliper.On the bushing now you open your new hole for connect the caliper to the car.
i hope to explain correctly the procedure for the new hole.
regards to all