Neck bushing measurements?

[philip brousseau]

I have about a dozen neck sizing bushings and all of them measure out with my dial caliper as being. 003 to. 004 smaller than the number on the bushing? What am I missing here?

 

[rwj]

Respectfully; calipers will not provide accurate measurements when used on small diameter holes. I recommend using either gauge pins or an expanding ball gauge with an OD micrometer.

https://www.mscdirect.com/product/details/86425378

 

[coldboreshot]

Ball micrometer. Flat edges on an inside radius does not mix.

 

[Edd]

I have about a dozen neck sizing bushings and all of them measure out with my dial caliper as being. 003 to. 004 smaller than the number on the bushing? What am I missing here?

If your bushing ID is .300" and your caliper jaw width is 1/32" your measurement will be .0017" small. If the caliper jaws are wider or the bushing ID is smaller, the measurement will be off by a larger amount.

 

[philip brousseau]

Thank you all. I understand what you're saying.