Several of the American Society of Mechanical Engineers (ASME) standards appendices contain two different types of gauges for determining part straightness. One gauge is an attribute-type of thread runout gauge consisting of a special threaded ring gauge attached to a cylinder which is set with a special setting master.
The second gauge is an attribute-type camber or bow measuring gauge consisting of a base plate with one stationary side rail and one adjustable side rail. The gap between the rails is set with a pair of micrometer heads.
The ASME B18 sub-committees are in the process of removing the thread runout gauge and leaving only the camber gauge in the various screw and bolt standards. This action is being taken because the sub-committee members feel the rail-type camber gauge is as likely to detect objectionably bent screws and bolts as well as the runout-type gauge, but the rail-type gauge is much more versatile and cost-effective.
Most of the ASME standards are consistent in their straightness specifications. Screws and bolts up to and including 12’ in length can be bowed 0.006” per inch of length. Parts exceeding 12’ can be bowed 0.008” per inch of length. If a user’s application requires a part straighter than these limits, it must specify the required straightness limits on the print and/or purchase order.
