Thread Designations
A thread designation is the shorthand code that fully identifies a screw thread on a drawing or parts list — the thread family, its size, pitch, and sometimes its tolerance class, all packed into a single string like M10x1.5 or 3/8-16 UNC. Reading these correctly matters: mixing up a fine and coarse pitch, or a UNC and UNF thread of the same nominal diameter, produces a fastener that looks right but won't actually thread into its mating part.
The chart below covers the designation formats used by the major thread standards referenced elsewhere on this site — ISO metric, Unified (UNC/ UNF/UNEF), British imperial (BSW/BSF), and trapezoidal/Acme threads — along with the common names and abbreviations you'll see used for each in practice.
| ISO or ANSI Designation | DESCRIPTION | Ref. ANSI, BS, ISO |
|---|---|---|
| ACME C | Acme Threads, Centralizing | B1.5 |
| ACME G | Acme Threads, General Purpose | B1.5 |
| AMO | American Standard Microscope Objective Threads | B1.11 |
| ANPT | Dryseal Special Taper Pipe Threads | B1.20.3 |
| AWWA | Underground Service Line Valves and Fittings | C800-84 |
| BA | British Screw Threads | BS.57 |
| BSF | British Parallel Screw Threads | BS.84 |
| BSW | British Parallel Screw Threads | BS.84 |
| BUTT | Buttress Threads, Pull Type | B1.9 |
| DIN | German Specifications | - |
| F-PTF | Dryseal Fine Taper Threads Series | B1.20.3 |
| G | Straight Pipe Threads | BS.2779 |
| ISO | International Standard Organization | - |
| JIS | Japanese Industrial Standard | - |
| M | Metric Screw Threads-M Profile with Basic ISO 68 Profile | B1.13M B1.18M |
| MJ | Metric Screw Threads-MJ Profile with Rounded Root of Radius 0.15011P to 0.18042P | B1.21M |
| MJS | Metric Screw Threads-MJ Profile Special Series | B1.21M |
| NC5 | Class 5 Interference Fit External Threads | B1.12 |
| NC5 | Class 5 Interference Fit Internal Threads | B1.12 |
| NC5 IF | Entire Ferrous Material Range | B1.12 |
| NC5CSF | For Driving Copper Alloy and Soft Ferrous Material of 160 Bhn or Less | B1.12 |
| NC5HF | For Driving in Hard Ferrous Material of Hardness over 160 Bhn | B1.12 |
| NC5ONF | For Driving in Other NonFerrous Material (Nonferrous Materials Other Than Copper Alloys, Any Hardness | B1.12 |
| NCF INF | Entire Nonferrous Material Range | B1.12 |
| NFPA 1963 | Fire Hose Threads | - |
| NGO | National Gas Outlet Threads | CGA V-1 |
| NGS | National Gas Straight Threads | CGA V-1 |
| NGT | National Gas Taper Threads (See Also SGT) | CGA V-1 |
| NH | American Standard Hose Coupling Threads of Full Form | B1.20.7 |
| NHR | American Standard Hose Coupling Threads for Garden Hose Applications | B1.20.7 |
| NPSC | American Standard Straight Pipe Threads in Pipe Couplings | B1.20.1 |
| NPSF | Dryseal American Standard Fuel Internal Straight Pipe Threads | B1.20.3 |
| NPSH | Dryseal American Standard for Hose Coupling Joints with Straight Internal External Loose Fitting Thread | B1.20.7 |
| NPSI | Dryseal American Standard Intermediate Internal Straight Pipe Threads | B1.20.3 |
| NPSL | Aeronautical National Form Taper Pipe Threads | MIL P-7105B |
| NPSM | American Standard Straight Pipe Threads for Free-Fitting Mechanical Joints for Fixtures | B1.20.1 |
| NPT | American Standard Taper Pipe Threads for General Use | B1.20.3 |
| NPTF | Dryseal American Standard Taper Pipe Threads | B1.20.3B |
| PTF SAE | Dryseal SAE Short Taper Pipe Threads | B1.20.3 |
| PTF SPL | Dryseal Special Short Taper Pipe Threads | B1.20.3 |
| PUCH BUTT | Buttress Threads , Push Type | B1.9 |
| R | British Taper Pipe Threads | BS.21 |
| Rc Rp | British Taper Pipe Threads | BS.21 |
| SGT | Special Gage Taper Threads | BS.21 |
| SPL PTF | Dryseal Special Short Taper Pipe Threads | B1.20.3 |
| STUB ACME | Stub Acme Threads | B1.8 |
| UN | Unified Inch Screw Thread, Constant-Pitch Series | B1.1 |
| UNC | Unified Inch Screw Thread, Coarse-Pitch Series | B1.1 |
| UNEF | Unified Inch Screw Thread, Extra-Fine Series | B1.1 |
| UNF | Unified Inch Screw Thread, Fine-Pitch Series | B1.1 |
| UNJ | Unified Inch Screw Thread, Constant-Pitch Series with Rounded Root of Radius 0.15011P to 0.18042P | B1.15 |
| UNJEF | Unified Inch Screw Thread, Fine-Pitch Series, with Rounded Root of Radius 0.15011P to 0.18042P | B1.15 |
| UNJF | Unified Inch Screw Thread, Coarse-Pitch Series, with Rounded Root of Radius 0.15011P to 0.18042P | B1.15 |
| UNM | Unified Miniature Thread Series | B1.10 |
| UNR | Unified Inch Screw Thread, Constant-Pitch Series, with Rounded Root of Radius Not Less Than 0.108P | B1.1 |
| UNRC | Unified Inch Screw Thread, Coarse-Pitch Series, with Rounded Root of Radius Not Less Than 0.108P | B1.1 |
| UNRE | Unified Inch Screw Thread, Extra-Fine Pitch Series, with Rounded Root of Radius 0.15011P to 0.18042P | B1.15 |
| UNREF | Unified Inch Screw Thread, Extra-Fine Pitch Series, with Rounded Root of Radius Not Less Than 0.108P | B1.1 |
| UNRF | Unified Inch Screw Thread, Fine-Pitch Series, with Rounded Root of Radius Not Less Than 0.108P | B1.1 |
| UNS | Unified Inch Screw Thread, Special Diameter Pitch, or Length of Engagement | B1.1 |
COMMON THREAD NAMES AND ABBREVIATIONS
THREAD DESIGNATIONS
| THREAD DESIGNATIONS | |
|---|---|
| DESIGNATION | DESCRIPTION |
| ACME 60° STUB | 60° Stub thread form |
| ACME STUB | Stub Acme thread form |
| ACME-C | Acme thread - centralizing |
| ACME-G | Acme thread, general purpose |
| AN | Army and Navy thread |
| ANPT | Aeronautical National Form taper pipe thread |
| AWWA | American Water Works Association |
| BA | British Association Standard thread form |
| BSB | British Standard Brass thread |
| BSC | British Standard Cycle thread |
| BSF | British Standard Fine thread series |
| BSPP | British Standard Pipe Parallel |
| BSPT | British Standard Pipe Taper |
| BSW | British Standard Whitworth |
| CEI | Cycle Engineers Institute Thread |
| CHT | Chemical Hose thread |
| GHT | Garden Hose thread |
| GPI | Glass Packing Institute Thread |
| MM | ISO Metric thread form |
| MJ | Metric Aerospace thread |
| N BUTT | American Buttress screw thread |
| NC | American National Coarse thread series |
| NEF | American National Extra-Fine thread series |
| NF | American National Fine thread series |
| NGO | American National gas outlet threads |
| NGT | American National gas taper threads |
| NH | American National hose & fire hose coupling |
| NM | National Miniature thread series |
| NPS | American Standard straight pipe thread |
| NPSC | American Standard straight pipe thread in couplings |
| NPSF | American Standard internal straight pipe thread (dryseal) |
| NPSH | American Standard straight pipe thread for hose couplings & nipples |
| NPSI | American Standard intermediate straight pipe thread (dryseal) |
| NPSL | American Standard straight pipe thread for locknuts |
| NPSM | American Standard straight pipe thread for mechanical joints |
| NPT | American Standard taper pipe thread |
| NPTF | Dryseal American Standard taper pipe thread |
| NPTR | American Standard taper pipe thread for rail fittings |
| NS | Special threads of American National Form |
| Pg | Panzergewinde thread |
| PTF | Dryseal SAE Short Taper pipe thread |
| RMS | Royal Microscopical Society thread |
| SGT | Special Gas Taper thread form |
| SPL-PTF | Dryseal Short Taper Pipe thread |
| STI | Special Threads for Helical Coil Wire Screw Thread Inserts |
| UN | Unified and American thread series |
| UNC | Unified and American Coarse thread series |
| UNEF | Unified and American Extra-Fine thread series |
| UNF | Unified and American Fine thread series |
| UNIV | Unified Miniature Thread Series |
| UNJ | Unified Thread Series with Controlled Root Radius |
| UNJC | Unified Coarse Thread Series with Controlled Root Radius |
| UNJF | Unified Fine Thread Series with Controlled Root Radius |
| UNR | Unified Constant Pitch thread series with Controlled Root Radius |
| UNRC | Unified Coarse Thread Series with Controlled Root Radius |
| UNRF | Unified Fine Thread Series with Controlled Root Radius |
| UNS | Unified and American threads of selected special diameters and pitches |
| V | Tyre Valve thread |
RELATED PAGES
- Metric Thread Dimensions
- Unified Threads (UNC/UNF/UNEF)
- Thread Equivalents
- Trapezoidal Thread Dimensions
- Engineering Glossary — Thread Designation
FREQUENTLY ASKED QUESTIONS
What does the "x" mean in a metric thread designation like M10x1.5?
It separates the nominal diameter from the pitch — M10x1.5 means a 10mm nominal diameter thread with a 1.5mm pitch. If the pitch is left out entirely (just "M10"), the standard coarse pitch for that diameter is assumed. See Metric Threads for the full coarse and fine pitch tables.
What's the difference between UNC and UNF?
Both are Unified inch threads to the same diameter series, but UNC (Unified National Coarse) has fewer threads per inch than UNF (Unified National Fine) at the same nominal diameter. UNC is the more common general-purpose choice; UNF is often used where a finer adjustment, higher strength in thin sections, or resistance to vibration loosening is needed. See Unified Threads for full size tables.
How do I know which thread standard a part uses?
If the part or drawing is marked with a designation, matching it against the formats on this page will tell you the standard. Without a marking, measuring the major diameter and thread pitch (or threads per inch) and comparing against the relevant size chart is the most reliable way to identify it.
Are metric and imperial threads ever interchangeable?
Not directly — even where a metric and imperial thread are very close in nominal size, the thread form, pitch, and flank angle differ enough that they won't mate safely. Always match the designation exactly, or use a thread equivalents chart to find the closest genuine match rather than assuming compatibility.
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