If you are into building small models or anything else that has small round parts, there always comes a time when you need to find the center of a small round object.  I have designed a small Center Finder that will find the center of any round object between 1/4 and 1 1/2 inches, or between 1/2 and 3 inches with the large size.  
Yes, I actually designed and build this in two different sizes.

                                   Center Finder Is Milled From 1/8 Inch 6061 T6 Aluminum  

It is very accurate, and easy to use.  Hold against the open angle on back and using a fine point scribe, scribe a line across the part. Turn the part 90 degrees and scribe again.  The scribe marks intersect at the exact center of the round piece.   

Here Is The Rear View Showing The Centering Angle

This Small Turned Part Shows Dead Center