Direct reading radius gauge

Claim 1

Apparatus adapted to indicate directly the numerical value of the radius of an object in one of the English and Metric systems of measurement, comprising: a Y-shaped frame including a base and two divergent legs extending outwardly therefrom, each of said legs having a planar surface arranged to face the other of said legs, said planar surfaces intersecting in a line perpendicular to the longitudinal extent of each leg, said base having a cylindrical opening therethrough, the axis of said opening being arranged to intersect said line of intersection and arranged to bisect the angle of divergence between said planar surfaces; and a micrometer head originally intended to read in the other of said English and Metric systems of measurement and having a sleeve mounted on said base about said opening, having a thimble rotatably mounted on said sleeve, and having a spindle associated with said sleeve and thimble and operative to move axially of said opening in response to rotational movement of said thimble relative to said sleeve, said spindle having a planar end face perpendicular to the axis of said opening, said sleeve and thimble having cooperative numerical scale elements representative of numerical quantities to be measured, said scale elements reading zero when said line of intersection lies in the plane of said spindle end face; and wherein the angle of divergence is selected such that the sine of half of said angle of divergence between said planar surfaces is substantially equal to the amount of a known radius divided by the amount of said known radius plus the amount of the extent of axial displacement of said spindle end face beyond said line of intersection when said cooperative scale elements indicate the number of said known radius.