BSP / NPT and Common Thread Sizes Guide
Parallel Internal and External threads are Fastening Threads and require the use of a gasket or cone seal. Tapered threads are Joining Threads and create a pressure tight seal when used with jointing compound or PTFE tape.
Pipe Thread Acronyms
- NPT : American Standard Pipe Taper Thread (National Pipe Thread)
- FPT : American Standard female Pipe Taper Thread
- NPSC : American Standard Straight Coupling Pipe Thread
- BSP : British Standard Pipe (can mean either BSPP or BSPT)
- BSPP : British Standard Pipe Parallel
- BSPT : British Standard Pipe Taper
- GHT : Garden Hose Thread
- G Thread : British Gas – Parallel (same as BSPP)
- R Thread : British Tapered (same as BSPT)
NPT – National Pipe Thread (US Standard)
Table Keys : NPS : Nominal Pipe Size (inches). TPI : Threads per inch
| | Outside Diameter |
| NPS | TPI | Inches | mm |
| 1/8” | 27 | 0.405 | 10.3 |
| ¼” | 18 | 0.540 | 13.7 |
| 3/8 | 18 | 0.675 | 17.15 |
| 1/2 | 14 | 0.84 | 21.34 |
| 3/4 | 14 | 1.05 | 26.67 |
| 1 | 11.5 | 1.315 | 33.40 |
| 11/4 | 11.5 | 1.660 | 42.16 |
| 11/2 | 11.5 | 1.90 | 48.26 |
| 2 | 11.5 | 2.375 | 60.33 |
| 21/2 | 8 | 2.875 | 73.03 |
BSP – British Straight and Tapered
Table Keys : NPS : Nominal Pipe Size (inches). TPI : Threads per inch
| | Outside Diameter |
| NPS | TPI | Inches | mm |
| 1/8” | 28 | 0.402 | 10.21 |
| ¼” | 19 | 0.531 | 13.49 |
| 3/8 | 19 | 0.677 | 17.2 |
| 1/2 | 14 | 0.839 | 21.31 |
| 3/4 | 14 | 1.059 | 26.90 |
| 1 | 11 | 1.327 | 33.71 |
| 11/4 | 11 | 1.669 | 42.39 |
| 11/2 | 11 | 1.902 | 48.31 |
| 2 | 11 | 2.374 | 60.30 |
| 21/2 | 11 | 2.996 | 76.10 |
Straight Pipes Standards
NPSC - American Standard Straight Pipe Threads in Pipe Couplings Couplings :
- ANSI B1.20.1 PIPE THREADS, GENERAL PURPOSE (INCH)
- FED-STD-H28/7 SCREW-THREAD STANDARDS FOR FEDERAL SERVICES SECTION 7 PIPE THREADS - GENERAL PURPOSE
NPSF - Dryseal American Standard Fuel Internal Straight Pipe Threads :
- SAE J476 DRYSEAL PIPE THREADS
- ANSI B1.20.3 DRYSEAL PIPE THREADS (INCH)
- FED-STD-H28/8 SCREW-THREAD STANDARDS FOR FEDERAL SERVICES SECTION 8 DRYSEAL PIPE THREADS
NPSI - Dryseal American Intermediate Internal Straight Pipe Threads :
- SAE J476 DRYSEAL PIPE THREADS
- ANSI B1.20.3 DRYSEAL PIPE THREADS (INCH)
- FED-STD-H28/8 SCREW-THREAD STANDARDS FOR FEDERAL SERVICES SECTION 8 DRYSEAL PIPE THREADS
NPSM - American Standard Straight Pipe Threads for Free-Fitting Mechanical Joints for Fixtures (these threads fit freely over NPTF threads. They are used in swivel nuts of 07 adapters) :
- ANSI B1.20.1 PIPE THREADS, GENERAL PURPOSE (INCH)
- FED-STD-H28/7 SCREW-THREAD STANDARDS FOR FEDERAL SERVICES SECTION 7 PIPE THREADS - GENERAL PURPOSE
Taper Pipe Standards
ANPT - Aeronautical National Taper Pipe Threads :
- MIL-P-7105 PIPE THREADS, TAPER, AERONAUTICAL NATIONAL FORM, SYMBOL ANPT, GENERAL REQUIREMENTS
NPT - American Standard Taper Pipe Threads for General Use :
- ANSI B1.20.1 PIPE THREADS, GENERAL PURPOSE (INCH)
- FED-STD-H28/7 SCREW-THREAD STANDARDS FOR FEDERAL SERVICES SECTION 7 PIPE THREADS - GENERAL PURPOSE
NPTF - Dryseal American Standard Taper Pipe Threads :
- SAE J476 DRYSEAL PIPE THREADS
- ANSI B1.20.3 DRYSEAL PIPE THREADS (INCH)
- FED-STD-H28/8 SCREW-THREAD STANDARDS FOR FEDERAL SERVICES SECTION 8 DRYSEAL PIPE THREADS
PTF - SAE Short is mainly used in low pressure pneumatic and fuel applications :
- ANSI B1.20.3 DRYSEAL PIPE THREADS (INCH)
PTF SPL - Short & SPL Extra Short - Dryseal Special Short Taper Pipe Threads. Used in some pneumatic components where shortened thread depth is required because of size limitations.:
- ANSI B1.20.3 DRYSEAL PIPE THREADS (INCH)
AWWA - American Water Works Association :
- ANSI/AWWA C800-05 UNDERGROUND SERVICE LINE VALVES AND FITTINGS
Unified Thread Standards
UN - Unified Constant Pitch Threads (standard series: 4, 6, 8, 12, 16, 20, 28, 32):
- ASME B1.1 UNIFIED INCH SCREW THREADS (UN & UNR THREAD FORM)
- FED-STD-H28/2 SCREW-THREAD STANDARDS FOR FEDERAL SERVICES SECTION 2 UNIFIED INCH SCREW THREADS-UN AND UNR THREAD FORMS
UNC - Unified Coarse Threads :
- ASME B1.1 UNIFIED INCH SCREW THREADS (UN & UNR THREAD FORM)
UNEF - Unified Extra Fine Threads:
- ASME B1.1 UNIFIED INCH SCREW THREADS (UN & UNR THREAD FORM)
- FED-STD-H28/2 SCREW-THREAD STANDARDS FOR FEDERAL SERVICES SECTION 2 UNIFIED INCH SCREW THREADS-UN AND UNR THREAD FORM
UNF - Unified Fine Threads :
- ASME B1.1 UNIFIED INCH SCREW THREADS (UN & UNR THREAD FORM)
- FED-STD-H28/2 SCREW-THREAD STANDARDS FOR FEDERAL SERVICES SECTION 2 UNIFIED INCH SCREW THREADS-UN AND UNR THREAD FORMS
UNS - Unified Special Pitch Threads:
- ASME B1.1 UNIFIED INCH SCREW THREADS (UN & UNR THREAD FORM)
- SCREW-THREAD STANDARDS FOR FEDERAL SERVICES-SEC. 3
UNJ - Unified Controlled Root Radius Threads :
- ANSI B1.15 UNIFIED INCH SCREW THREADS (UNJ THREAD FORM)
- FED-STD-H28/4 SCREW-THREAD STANDARDS FOR FEDERAL SERVICES SECTION 4 CONTROLLED RADIUS ROOT SCREW THREADS, UNJ SYMBOL
Metric Thread Standards
M - Metric Screw Threads M profile:
- ISO 261 ISO GENERAL PURPOSE METRIC SCREW THREADS - GENERAL PLAN
- ASME B1.13M METRIC SCREW THREADS: M PROFILE
- FED-STD-H28/21 METRIC SCREW-THREADS
M Keg - Metric Taper Threads (Mainly used in Germany):
- DIN 158-1 METRIC EXTERNAL TAPER SCREW THREADS AND MATING INTERNAL PARALLEL SCREW THREADS - PART 1. NOMINAL SIZES, LIMIT DEVIATIONS, LIMITS OF SIZE AND VERIFICATION
- DIN 158-2 METRIC EXTERNAL TAPER SCREW THREAD AND MATING INTERNAL PARALLEL SCREW THREADS - PART 2. GAUGING SYSTEM, USE OF GAUGES, CALCULATION OF GAUGE DIMENSIONS AND GENERAL FEATURES
BSi - British Standards
R (BSPT) - British Standard Taper Pipe Threads, External:
- BS 21 PIPE THREADS FOR TUBES AND FITTINGS WHERE PRESSURE-TIGHT JOINTS ARE MADE ON THE THREADS (METRIC DIMENSIONS)
- ISO 7/1 PIPE THREADS: DESIGNATION, DIMENSIONS/TOLERANCES
Rc (BSPT) - British Standard Taper Pipe Threads, Internal:
- BS 21 PIPE THREADS FOR TUBES AND FITTINGS WHERE PRESSURE-TIGHT JOINTS ARE MADE ON THE THREADS (METRIC DIMENSIONS)
- ISO 7/1 PIPE THREADS: DESIGNATION, DIMENSIONS/TOLERANCES
Rp or G (BSPP) - British Standard Pipe (Parallel) Threads:
- BS 2779 PIPE THREADS FOR TUBES & FITTINGS WHERE PRESSURE-TIGHT JOINTS ARE NOT MADE ON THE THREADS (METRIC DIMENSIONS)
- ISO 228/1 PIPE THREADS PT 1: DESIGNATION, DIMENSIONS, TOLERANC
Japanese Standards
PF - JIS - Parallel Pipe Threads. PF threads are functionally interchangeable with BSPP. This is an old designations replaced with G :
- JIS B 202 PARALLEL PIPE THREADS
- ISO 228/1 PIPE THREADS PT 1: DESIGNATION, DIMENSIONS, TOLERANCE
PT - JIS - Taper Pipe Threads. PT threads are functionally interchangeable with BSPT threads. This is an old designations replaced with and R and Rc :
- JIS B 0203 TAPER PIPE THREADS
- ISO 7/1 PIPE THREADS: DESIGNATION, DIMENSIONS/TOLERANCES
PS - JIS - Parallel Internal Pipe Threads (to mate with PT threads) :
- JIS B 0203 TAPER PIPE THREADS