With the following described measuring process you will determine the measures we need to manufacture your custom carb spacer. The measurement process is simple, but should still be performed as accurately as possible. Be aware, the more accurate you measure, the more accurate your carb spacer fit will ultimately be.
The first step is to print out the dimension chart of your carb spacer (usually 5 pages). 
Select your preferred unit of measurement (metric or inches).

Now start the measuring process with the 1st threaded hole (core diameter A). Repeat the measurement. When measuring internal diameters, always try to determine the largest values in each case. Enter the values step by step in the dimension table. In contrast to the measurement of inside diameters, when measuring the distances between holes, remember that the smallest possible dimension should be found here. When all measurements have been taken on the manifold, continue with the measurements on the carburetor. Make the measurements there in the same way as well. Finally, enter the desired thickness of your Carb Spacer in the table. Done? CONGRATULATIONS!!! You have now overcome the most difficult part.