Kinematic restraint

In a restraint apparatus for repeatedly connecting a precision instrument to a support frame in an identical position relative to said support frame, comprising a first plate secured to said support frame and having a generally horizontal planar surface, and a second plate secured to said instrument and having a generally horizontal planar surface, said horizontal planar surfaces of said first plate and said second plate facing one another and carrying means for providing six contact points, the improvement wherein three of said contact points are provided by contact means comprising three first convex spherical members secured to said facing surface of said first plate in a triangular array and a second convex spherical member secured to said facing planar surface of said second plate, said second convex spherical member being seated upon and simultaneously contacting each of said three first convex spherical members at a point and being spaced from said facing planar surface of said first plate, and two of said contact points are provided by contact means comprising two cylindrical members secured to said facing planar surface of said first plate in parallel relation to one another to define a channel parallel to said facing planar surface of said first plate and a third convex spherical member secured to the facing planar surface of said second plate, said third convex spherical member contacting each of said cylindrical members at a point along said channel and being spaced from said facing planar surface of said first plate.