External Supermicrometer A - Model A250, A375, A500, A625 - Obsolete
The Standard of Accuracy
Two models of the External Supermicrometer Model A were manufactured by Pratt & Whitney, the Mechanical Supermicrometer and the Electrolimit Supermicrometer. The two models were the same except for the tailstock. The Mechanical Supermicrometer uses a mechanical pressure tailstock and the Electrolimit Supermicrometer uses an Electrolimit pressure tailstock in conjunction with an indicating meter.
The Mechanical Supermicrometer is a basic measuring instrument suitable for the standards room or measuring laboratory when measuring accuracy to 0.0001 inch (2.5 micron) is required. An Electrolimit Supermicrometer, when used as a comparator, will give readings accurate to 0.00002 inch (0.5 micron). The Supermicrometer is constructed to withstand continuous use and may be used for production work in the shop either on a bench beside a machine or in the inspection area.
The External Supermicrometer Model B is a direct replacement to the External Supermicrometer Model A.
The External Supermicrometer Model C is a replacement to the External Supermicrometer Model A.
The External Supermicrometer Model PC is a replacement to the External Supermicrometer Model A.