This specification defines the inspection criteria and requirements in inches for gaging the head protrusion values for 100? flush head rivets and threaded fasteners; Type A - Rivets (i.e. NAS525). Type B - Externally threaded 100? Full Flush Head fasteners (i.e. NAS1580). Type C - Externally threaded 100? Reduced Flush Head fasteners (i.e. NAS1581). This specification includes the individual flush head protrusion gage block diameters@ the method for determining applicable individual gage block diameters and acceptable gage diameter wear factors. Recommendations for improvement and/or corrections to this standard practice document should be directed to an NASC Representative or to the National Aerospace Standards Committee Specifications herein@ of issue in effect on date of price inquiry@ are a part of this specification to the extent indicated. In the case of conflict@ the requirements herein shall take precedence. This Standard Practice takes precedence over documents referenced herein.