Mil-Spec purchasing terminology.

// PURCHASING TERMS

Language used on drawings and purchase orders

AN hardware

Army-Navy standards identify many aircraft hardware families. Each series has its own requirements and revision history.

MS hardware

Military Standard designations appear on drawings and purchase orders. Some remain active; others have moved to NASM or another standard.

NAS and NASM

NAS means National Aerospace Standards. NASM includes military-origin standards adopted into that system.

Series and dash number

A series identifies the hardware family. A dash number selects an item within that family; its meaning must be checked in the specific standard.

UNC and UNF

Unified coarse and fine thread series. Diameter, pitch and thread class must all match the specified requirement.

CRES

Corrosion-resistant steel. The term alone does not identify every material or processing requirement for a part.

Specification revision

The issue of a standard required by the drawing, purchase order or contract. Include an explicit revision requirement when one applies.

Document supersession

A standard has been replaced by another document. This relationship alone does not approve a complete part-number substitution.

Certificate of conformance

A declaration that the supplied product meets the identified requirements. Include required certificate details with the RFQ.

Lot traceability

Records connecting supplied hardware to its manufacturing or material lot as required by the order.

UNJ threads

A Unified thread form with a controlled external root profile. Do not assume that an ordinary UN thread and a UNJ callout are the same requirement.

Thread class

A tolerance-class designation such as 2A, 3A or 3B. The number and the external/internal letter are both part of the callout.

Grip length

The unthreaded portion or clamping-range measure defined for a particular fastener family. Confirm the standard’s own convention.

Shoulder diameter

The diameter of the smooth locating or bearing portion of a shoulder screw, separate from its male thread size.

Shoulder length

The smooth shoulder’s axial length. It is distinct from thread length and overall length.

Countersink angle

The included angle of a countersunk head and its mating seat. An 82-degree and a 100-degree callout should be kept distinct.

Pan head

A head configuration that sits above the bearing surface rather than seating in a countersink.

Fillister head

A raised cylindrical-style screw head. Preserve any drilled-head or drive detail in the full designation.

Socket drive

An internal driving recess. A common drive does not establish the same head, material or performance requirement.

Cup point

A set-screw point form. It must be distinguished from flat, cone and dog-point configurations.

Half-dog point

A projecting set-screw point configuration. Its geometry is part of the selection, not a cosmetic difference.

Dowel pin

A solid locating pin used with a specified fit. Diameter tolerance and end geometry must agree with the application.

Slotted spring pin

A tubular pin with a longitudinal slot. Its free-state dimensions and mating-hole requirements differ from those of a solid dowel.

Coiled spring pin

A rolled, multilayer spring-pin construction. Duty classification is part of the family selection.

Cotter pin

A split retaining pin. It is a different item from the headed pin or drilled fastener it may retain.

Keylocking insert

A threaded insert mechanically retained by keys. Internal locking of the screw thread is a separate feature.

Helical insert

A wire-form threaded insert. Free-running and screw-locking configurations have different requirements.

Rivet nut

An internally threaded component installed in a prepared hole using a specified process. Open/closed end and head configuration matter.

Nutplate

A nut configured for attachment to a structure. Lug arrangement, floating/fixed design and locking construction should remain in the callout.

Prevailing torque

Resistance associated with a locking-thread feature. Acceptance limits come from the applicable specification, not this glossary.

Internal retaining ring

A ring intended for a groove in a bore. Groove and ring geometry must be reviewed together.

External retaining ring

A ring intended for a groove on a shaft. A shared shaft size does not establish identical ring section or thickness.

Spacer

A component with a through opening used to establish separation. Bore, outside dimensions and length define its envelope.

Standoff

A spacing component with threaded or installation interfaces. Male/female and swage configurations are distinct.

Swage mounting

An attachment method that deforms a mounting feature. The required hole and installation process must match the selected component.

Passivation

A surface treatment for specified corrosion-resistant materials. It does not identify the complete material grade or finish requirement by itself.

Cadmium plating

A specified coating that can appear in military hardware requirements. The applicable coating callout, class and processing requirements must be retained.

Dry-film lubricant

A specified surface-applied lubricant. Its presence can be controlled separately from the base coating.

A286

An iron-based high-temperature alloy designation used in aerospace hardware. Product condition and processing requirements remain specification-specific.

Lot number

An identifier linking material or finished goods to a defined batch. Required lot records should accompany the order documentation.

Manufacturer certificate

Documentation from the manufacturing source. This is distinct from a distributor’s own conformance declaration.

Source restriction

An order or drawing requirement limiting eligible manufacturing sources. Submit it with the RFQ before sourcing begins.

NSN

National Stock Number, a supply-system identifier. It is not the same field as a manufacturer part number or military drawing designation.

CAGE code

An identifier for a specific organization or facility in government supply systems. It does not by itself certify a component’s conformity.

Inactive for new design

A document-use status distinct from cancellation. Review the actual record and procurement requirements.

Approved alternate

A different part accepted by the responsible authority for the stated use. Catalog similarity alone does not create that approval.

// APPLICATION

Use the terminology with the full designation

This glossary supports reading and quoting a requirement. It is not a universal part-number decoder or an installation instruction. Series-specific guides explain numerical and suffix examples in context.