This specification defines the inspection criteria and requirements for gaging the head protrusion values for 100??lush head fasteners and 100??lush head rivets The specification includes the requirements for three types of fasteners as follows: Type A - Rivets (?.e. NAS525). Type B - Externally threaded 100??ull Flush Head fasteners (i.e. NAS1580). Type C - Externally threaded 100??educed Flush Head fasteners (i.e. NAS1581). This specification includes the values of the protrusion gage block diameters to be utilized in gaging fastener head protrusion and the method for verifying the individual gage diameters. Recommendations for improvement and/or corrections to this specification 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.