Abstract: An apparatus for measuring the elevation of the head of a flush head countersunk fastener (e.g., a bolt or a rivet) before installation, is disclosed. Fasteners (21) to be measured are dropped, one at a time, into a precisely sized hole (69a or 69b) in a split gauge block (63) such that the heads of the fasteners protrude above the upper surface of the gauge block. The magnitude of head protrusion or elevation above the upper surface of the gauge block is measured by a head elevation measuring instrument (43). If the measured value lies within an acceptable range, a signal suitable for use in controlling the countersink depth of the hole that is to receive the fastener is produced and the fastener is forwarded to a fastener insertion machine. If the measured value lies outside of the acceptable range, the fastener is rejected.