"GENERAL: INTRODUCTION: Only with perfect splines can the theoretical tooth thickness@ dimensions (over pins or otherwise)@ gages@ and the resultant fits be in complete agreement. In actual practice@ the errors are relatively large and discrepancies are troublesome. If tooth thickness on the shaft and space width in the hole are correct@ then any errors of form or spacing will interfere unless the errors of both members match exactly@ which is improbable. An imperfectly splined shaft@ if snug in a ring gage@ is necessarily undersize at all except the few points of contact; likewise an internal spline that fits its plug gage must be oversize at most points@ the two parts then will almost certainly fit together looser than predicted by the gages. Note that@ in general the actual fit will be tighter than predicted by measurements over pins@ or by calipers@ but looser than indicated by plug and ring gages@ and the discrepancy will be of the same order of magnitude as the errors. For these reasons@ the plug gages must be undersize and the ring gages fitted to representative master plugs in order to control parts more satisfactorily within specified dimensions. Note also that the plug and ring gages covered here are not suitable for checking individual tooth or space dimensions. For that purpose special methods are necessary@ usually involving direct measurements over pins@ with calipers or by specialized apparatus. External spline elements are easier to produce@ control and check than internal splines. For this reason@ the ""Go"" and ""Not Go"" ring gages are customarily made to fit the master plug gages. PRODUCTION GAGING: The gaging practice presented in this ARP 179 employing plug and ring gages is intended to find the greatest application to the gaging of splines in quantity production where the cost of the recommended gages can be justified. For suggestions regarding gaging on experimental parts or small quantity manufacturing@ see section 7."