These 2-Step Dovetail Jaws have been superseded by the current 100mm Dovetail Jaws. they have been designed to mount bowls by expanding into a recess or clamping onto a spigot.  The perfect circle measurements are as follow: The outside diameter is 100mm which is tapered as seen in photo 2. The inside two diameter are 84mm & 74mm. These jaws have a nickle plated finish.