What are Gage Balls (aka Ball Gages)?

Fowler Gage Ball Set, 52 piece.  About $71.02 on Amazon…

Ball Gages or Gage Balls, as the name suggests, are precision ground balls in specific accurately made diameters.  They’re usually made of hardened chrome steel, but ceramic balls are also available.  A set comes with a variety of ball sizes.  They’re handy for a variety of inspection applications, but typically you’ll need to be a bit handy with math to use your ball gages.

For example, this diagram shows how to use a Gage Ball to measure the major diameter of a countersink:

Ball Gage Calculator in G-Wizard

That last countersink example is one of two ball gage calculators that are included with a G-Wizard Machinist’s Calculator.  It looks like this:

The Calculator is dead simple to use.  Simply enter the Ball dia, measured height, and if using the countersink calculator the angle and the resulting diameter at the edge will be displayed.  BTW, you’re welcome to continue using the geometry calculator after the free trial expires.  Just consider it our gift to you for signing up;

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More Gage Ball Math

As another example, consider using two Gage Balls to measure a taper angle:

Example courtesy of Math Encounters Blog…

One can also use Gage Balls to measure the diameter of a bore like this:

Bore diameter example courtesy of Math Encounters Blog…

Ball Plug Gages

Loose precision balls can be a pain to manage.  If your application allows, ball plug gages are often more convenient:

A typical go/no-go ball plug gage…

Ball Plug Gages simplify handling by introducing a handle, and they also typically come in go / no-go pairs of gage balls.