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Distributor's Link Magazine Spring 2023 / Vol 46 No 2


44 THE DISTRIBUTOR’S LINK Larry Borowski President GREENSLADE & COMPANY INC. 2234 Wenneca Avenue, Fort Worth, TX 76102 TEL 817-870-8888 FAX 817-870-9199 EMAIL WEB SETTING ADJUSTABLE THREAD RINGS PART 1: WHY DO I NEED THE SET PLUG? Oftentimes we are sent special sized GO and NOT GO adjustable threaded ring gages for calibration, or we are asked to quote/manufacture new ones. In either case we must ask the customer if they own the set plug, and, in most cases, they do not. The most common response we get is, “Why do I need the set plug? The last company I sent these gages to didn’t require them.” Upon further investigation, it is found that the “other company” is using some form of direct measurement, either CMM or single point ball probes. The simple fact is that the “other company” is not following the consensus standards that govern this calibration, and in turn is misleading end users to believing their calibrations are valid and proper. Several standards are quite clear on how adjustable thread rings are to be checked, set, adjusted, or calibrated: ¤ ASME B1.2 and ASME B1.16 state: Adjustable GO (and subsequently NOT GO) thread ring gages must be set to the applicable W tolerance setting plugs. ¤ MIL-STD-120 states: The pitch diameter of adjustable thread ring gages is adjusted by fitting the ring to a setting plug of known size. ¤ FED-STD-H28/6A states: The size of adjustable limit or indicating thread gages is controlled by utilizing the applicable W tolerance thread setting plug. ¤ IFI-301 states: The functional diameter of the working ring is set to the functional diameter size of the combined characteristics of the setting plug. TECHNICAL ARTICLE It is abundantly clear in all the standards that govern thread gaging that a set plug is required to set an adjustable ring gage. A few points that may help explain the reasoning and difference between setting a ring gage to a set plug verses directly measuring the pitch diameter are: ¤ Adjustable thread rings are not round. A set plug will engage the circular boundary, but a direct measure probe will simply measure (2) or more independent points in the thread groove, and chances are pretty good that the “best ball” size is not being used. ¤ Adjustable thread rings are intended to be used as a functional check of the product. Set plugs will confirm a functional fit, but direct measurement will only provide pitch diameter size at the specific thread groove that is probed. Direct measurement does not take factors such as flank angle, lead, root clearance, or helical offset into consideration. In other words, all the elements that make up functional fit are being ignored. CONTINUED ON PAGE 120


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