Ball Bearing Size

[kenbeth]

Does anyone know the diameter of the ball bearing in a thk hsr 20
bearing block I have measured mine and have found one ball smaller
than the rest , as i have brought off ebay i am not sure if they have been replaced with a wrong size .

sizes measured are 3.969mm plus one at 3.175mm

[Torsten]

Just guessing but could it be that the smaller ball is
just used as a spacer.
May not be enough room for one of the proper size?