[Austin W Hogan]

Indexed screws are a quality control technique in many precision industries. Indexed screws indicate a job is complete; unindexed screws are the sign of trial fittings and work in progress. Indexed screws were the mark of anything installed by the Flight Test Instrumentation Department when I worked in that department at Grumman.
I later worked with a superior instrument maker, Bill Winter, who indexed every screw and fitted every surface with airtight quality. The man he learned from, George Gardner, chief of the GE General Engineering Lab instrument shop fitted things as precisely but applied a unique test. After calibrating an instrument, he removed all the nuts bolts and screws, then replaced them with parts from the salvage box. If the instrument repeated the calibration he approved its delivery.

Best, Austin