Standardization

Standardization of screw threads has evolved since the early nineteenth century to

facilitate compatibility between different manufacturers and users. The standardization

process is still ongoing; in particular there are still (otherwise identical) competing

metric and inch-sized thread standards widely used.[6]

Standard threads are commonly

identified by short letter codes (M, UNC, etc.) which also form the prefix of the

standardized designations of individual threads.

Additional product standards identify preferred thread sizes for screws and nuts, as well

as corresponding bolt head and nut sizes, to facilitate compatibility between spanners

(wrenches) and other tools.

ISO standard threads

Main article: ISO metric screw thread

The most common threads in use are the ISO metric screw threads (M) for most

purposes and BSP threads (R, G) for pipes.

These were standardized by the International Organization for Standardization (ISO) in

1947. Although metric threads were mostly unified in 1898 by the International

Congress for the standardization of screw threads, separate metric thread standards were

used in France, Germany, and Japan, and the Swiss had a set of threads for watches.

Other current standards

In particular applications and certain regions, threads other than the ISO metric screw

threads remain commonly used, sometimes because of special application requirements,

but mostly for reasons of backwards compatibility:

ASME B1.1 Unified Inch Screw Threads, (UN and UNR Thread Form),

considered an American National Standard (ANS) widely use in the US and

Canada

Unified Thread Standard (UTS), which is still the dominant thread type in the

United States and Canada. This standard includes:

o Unified Coarse (UNC), commonly referred to as "National Coarse" or

"NC" in retailing.

o Unified Fine (UNF), commonly referred to as "National Fine" or "NF" in

retailing.

o Unified Extra Fine (UNEF)

o Unified Special (UNS)

National pipe thread (NPT), used for plumbing of water and gas pipes, and

threaded electrical conduit.

o NPTF (National Pipe Thread Fuel)

British Standard Whitworth (BSW), and for other Whitworth threads including:

o British Standard Fine (BSF)

o Cycle Engineers' Institute (CEI) or British Standard Cycle (BSC)

British standard pipe thread (BSP) which exists in a taper and non taper variant;

used for other purposes as well

o British Standard Pipe Taper (BSPT)

British Association screw threads (BA), primarily electronic/electrical, moving

coil meters and to mount optical lenses

British Standard Buttress Threads (BS 1657:1950)

British Standard for Spark Plugs BS 45:1972

British Standard Brass a fixed pitch 26tpi thread

Glass Packaging Institute threads (GPI), primarily for glass bottles and vials

Power screw threads

o Acme thread form

o Square thread form

o Buttress thread

Camera case screws, used to mount a camera on a photographic tripod:

o ¼″ UNC[7]

used on almost all small cameras

o ⅜″ UNC for larger (and some older small) cameras

(many older cameras use ¼" BSW or ⅜" BSW threads, which in low stress applications,

and if machined to wide tolerances, are for practical purposes compatible with the UNC

threads)

Royal Microscopical Society (RMS) thread, also known as society thread, is a

special 0.8" diameter x 36 thread-per-inch (tpi) Whitworth thread form used for

microscope objective lenses.

Microphone stands:

o ⅝″ 27 threads per inch (tpi) Unified Special thread (UNS, USA and the

rest of the world)

o ¼″ BSW (not common in the USA, used in the rest of the world)

o ⅜″ BSW (not common in the USA, used in the rest of the world)

Stage lighting suspension bolts (in some countries only; some have gone entirely

metric, others such as Australia have reverted to the BSW threads, or have never

fully converted):

o ⅜″ BSW for lighter luminaires

o ½″ BSW for heavier luminaires

Tapping screw threads (ST) – ISO 1478

Aerospace inch threads (UNJ) – ISO 3161

Aerospace metric threads (MJ) – ISO 5855

Tyre valve threads (V) – ISO 4570

Metal bone screws (HA, HB) – ISO 5835

Panzergewinde (Pg) (German) is an old German 80° thread (DIN 40430) that

remained in use until 2000 in some electrical installation accessories in

Germany.

Fahrradgewinde (Fg) (English: bicycle thread) is a German bicycle thread

standard (per DIN 79012 and DIN 13.1), which encompasses a lot of CEI and

BSC threads as used on cycles and mopeds everywhere

(http://www.fahrradmonteur.de/fahrradgewinde.php)

CEI (Cycle Engineers Institute, used on bicycles in Britain and possibly

elsewhere)

Edison base Incandescent light bulb holder screw thread

Fire hose connection (NFPA standard 194)

Hose Coupling Screw Threads (ANSI/ASME B1.20.7-1991 [R2003]) for garden

hoses and accessories

Löwenherz thread, a German metric thread used for measuring instruments

Sewing machine thread