Measuring plug 1 is inserted into the bore of work 2. Axial channel 3 is connected to the measuring chamber from which compressed air is delivered to the plug and where its pressure is measured. The plug contains bushing 4 whose tip a contacts the bore surface of work 2. Sliding in the bushing is plunger 5 into which ball-head pin b is pressfitted. Pin b contacts the bore surface opposite tip a. Plunger 5 is tapered and partly closes air outlet orifice c. Depending upon the size of the bore diameter of the work, the plunger opens the air outlet orifice the corresponding amount. This is used to measure the bore diameter.
$3734$SHP,M$