d. GO NO-GO: the gaging of the Hexlobe ® recess is accomplished by using a GO NO-GO plug gage. The geometry of the recess has two diameters, an inscribed diameter, and a circumscribed diameter. The profile between these diameters is made up of many arcs. These gages are important to the manufacturer because it ensures the correct size of the recess as opposed to the penetration depth. The tolerance of the fastener, depending on the size of the recess can range anywhere from 0.003” (HL10) to 0.007 (HL55). The gaging elements tolerance is typically 0.0003” – 0.0006”. There are two types of gage elements, the final inspection, and the in-process. The sizes of the final inspection element are smaller than the In-Process element. The reasoning behind this is that the manufacturing operation uses the tighter tolerance which ensures that the final product meets the end specification.
3. Calibration of Gaging: the gages mentioned above need to be maintained and calibrated at a frequency defined by use. When calibrating a penetration gage it is not only important to calibrate the indicator but the gaging element as well. To calibrate either of the gaging elements listed above, very specialized measuring equipment needs to be used in an environment that is controlled for temperature and humidity. Optimally, the manufacturer will use a laboratory that is accredited to ISO17025. This standard ensures the competency of the laboratory to perform a calibration that falls within a certain measurement uncertainty. By doing this the manufacturer will greatly increase their ability to capably manufacture product at a high confidence level and minimize poor quality.
4. Driver Bit Gage: The driver bit gage is used for ensuring that the profile is within specification of the size driver bit being manufactured. Again, this gage is precision made and matches the cross-recess profile of the geometry opposite the external plug gage. The driver bit is inserted into the recess and the “G” width needs to fall within a 0.010” step built into the gage. See Illustration (F).
Driver Bit Profile (Ring) Gage