on dial 36 are made for a statistical universe of tubular members a bell shaped curve will result likewise a statistical universe of box ends measured in accordance with the procedure illustrated in fig5 will also result in a bell shaped curve for the indications recorded from dial gauges 48 and 49 the tubular members which are selected to be too far away from the center point of these curves may be rejected as selected by the operator of the gauges just described moreover it may be seen that by selectively choosing the tubular members from the tabulations a maximum optimizing of fits may be made it has been found that such selection by a statistical analysis of the measured data can result in a three to four fold improvement in overall tolerances than nonselected fitting of the box ends and pin ends now referring to fig6 it is first assumed that a ring gauge is made in a manner which is similar to ring gauge 12 previously described up to the step of grooving to receive the dial gauges this ring gauge however is to be made into a taper gauge and is identified in fig6 as ring taper gauge 50 when this gauge is screwed.