<http://schema.org/description>
"&lt;p&gt;A master ring, or ring gage, is basically a bore of known dimension.  The precision hole is often used as a setting master for variable ID gages (such as bore gages, air tooling and mechanical plug gages), for go/no-go mastering of fixed ID gages and for go/no-go OD inspection of male cylindrical workpieces. &lt;/p&gt;"^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.mmsonline.com/columns/calibrating-gages-with-master-and-engagement-rings-size-matters>