Ball Plug Gages

A Ball Plug Gage will measure the true cylindrical diameter of any hole.   The Ball Plug Gage will measure the cylindrical diameter of a hole absolutely.   If the Ball Plug Gage goes through a hole, we know that the hole diameter is at least as large as the ball that passes through it.  A lack of cylindrisity does not influence the Ball Plug Gages ability to measure true cylindical diameter. Even if a cylindrical hole is bent or cambered, a ball gage will still faithfully measure the true cylindrical diameter of that hole.