How calculate the disc hole dimensions?

Section 1:

Measure the diameter of the holes first.

Measure 1: 8,17mm
Measure 2: 8,20mm
Measure 3: 8,16mm 

it's approximately 8,17mm.

Section 2:

Always measure the diagonal holes to find the center-to-center hole measurement.

Measure the two holes diagonally from outside to outside.


Measure 1: 86,17mm
 

To find the Center-to-Center measure, apply the formula below.

Distance Between Center = Diagonal Outer Measurement - Hole Diameter

Distance Between Center = 86.17 - 8.17 = 78.00mm