NPFC - FED-STD-H28/5
SCREW THREAD STANDARDS FOR FEDERAL SERVICES, SECTION 5, UNIFIED MINIATURE SCREW THREADS
|Publication Date:||31 March 1978|
This section presents a thread series known as Unified Miniature Screw Threads and is intended for general purpose fastening screws and similar uses in watches, instruments, and miniature mechanisms. The series covers a diameter range from 0.30 to 1.40 mm (0.0118 to 0.0551 in) and thus supplements, the Unified thread series that begin at 0.060 in.
The 14 sizes are systematically distributed providing a uniformly proportioned selection over the entire range. They are alternately separated into two categories. The primary sizes are selections made in the interest of simplification and are those to which it is recommended that usage be confined whenever the circumstances of design permit. For more restrictive conditions, the secondary sizes are available.
The diameter-pitch combinations have been determined to provide both maximum strength against stripping and optimum conditions for manufacture on an interchangeable basis.
The values of all dimensions are supplied in both metric and inch units. The standard being basically metric, only the metric values of the nominal diameters and pitches are rational. Consequently, metric units are stipulated for all formulas and the inch dimension derived by conversion of the unrounded metric values, using the conversion factor 25.4 mm/in.
Use of this series is recommended on all new products in place of the many improvised and unsystematized sizes now in existence that have, never arrived at broad acceptance nor recognition by any standardization bodies.