1/8" BSPT Thread
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1/8" BSPT Thread (R 1/8") – British tapered thread in hydraulics and pneumatics
1/8" BSPT thread (short for British Standard Pipe Tapered, designation R 1/8" for tapered external male thread and Rc 1/8" for internal female thread) is a standardized British tapered pipe thread with a Whitworth profile according to ISO 7-1, DIN 2999, BS 21, and EN 10226\. It is widely used in hydraulic micro-installations, industrial pneumatics, central lubrication systems, measuring equipment, and machine construction. It features a tapered profile converging at a 1:16 (6.25%) ratio and a thread flank angle of 55°. The connection seal is formed directly on the thread turns by mechanically pressing the male cone (R 1/8") into a tapered (Rc 1/8") or cylindrical (G 1/8" / Rp 1/8") socket. For the 1/8" BSPT size, the thread pitch is 28 turns per inch (28 TPI / pitch \~0.907 mm). The external diameter of the male thread measured with a caliper ranges from 9.3 mm to 9.7 mm, while the internal diameter of the female thread is from 8.5 mm to 8.9 mm. The 1/8" BSPT thread is a common connection standard in pressure gauges, pressure sensors, pressure switches, control valves, and small actuators of European and Asian production.
Application and technical characteristics of the 1/8" BSPT thread
Fastening components, adapters, and crimped ends with 1/8" BSPT tapered thread (AGR-K / C31) are used in pressure circuits where a reliable, self-sealing threaded connection resistant to high pressures, vibrations, and operating temperature fluctuations is required.
- Tapered sealing profile (1:16 taper): Enables sealing directly on the thread turns using PTFE tape or liquid anaerobic sealant.
- British Whitworth thread angle 55°: A standard characteristic of European pipe threads, distinguishing it from the American 1/8" NPT tapered thread (where the angle is 60° and the pitch is 27 TPI).
- Precise caliper measurement dimensions: The external diameter of the male thread is 9.3–9.7 mm, and the female thread is 8.5–8.9 mm at a pitch of 28 turns per inch.
- Wide compatibility in control equipment: Commonly used in pressure gauges, pressure switches, pressure sensors, lubrication systems, and pneumatic devices.
- Wide selection of fittings and adapters: The offer includes straight fittings, elbows, tees, reductions, and hose ends (AGR-K) with 1/8" BSPT thread.
Why choose components with 1/8" BSPT thread from the HYDRON store?
All fittings, adapters, and ends with 1/8" BSPT thread offered by the HYDRON store are manufactured according to strict ISO 9001 quality standard procedures from free-cutting steel protected with an anti-corrosion zinc coating, as well as AISI 316L stainless steel and brass. Correct identification of the thread with a caliper is essential during service work – a common mistake is confusing the 1/8" BSPT tapered thread with the American 1/8" NPT thread (difference in pitch 28 TPI vs 27 TPI and angle 55° vs 60°) or metric M10x1, which leads to loss of tightness and destruction of the thread. In turn, distinguishing BSPT (tapered) from BSPP (cylindrical G 1/8") allows for choosing the correct sealing method. For the construction and service of hydraulic and pneumatic installations, we recommend selecting other compatible products from our range, such as crimped hydraulic hoses and pipes, precise pressure gauges, durable hydraulic quick couplers and extensive hydraulic valves.
Technical specification
Technical parameter | Value / Description |
|---|---|
Thread designation | 1/8" BSPT / R 1/8" (male tapered) / Rc 1/8" (female tapered) |
Manufacturing standards | ISO 7-1, BS 21, DIN 2999, EN 10226 |
External diameter of male thread (caliper) | 9.3 mm – 9.7 mm |
Internal diameter of female thread (caliper) | 8.5 mm – 8.9 mm |
Thread pitch (number of turns per inch) | 28 turns per inch (28 TPI / pitch \~0.907 mm) |
Thread profile angle and taper | Angle 55° (Whitworth), 1:16 taper (6.25% convergence) |
Sealing method | Sealing on the thread using PTFE tape or liquid anaerobic adhesive |
Available materials and coating | Free-cutting/forged steel, electro-galvanized, AISI 316L stainless steel, brass |
Frequently Asked Questions (FAQ)
How to measure a 1/8" BSPT thread with a caliper?
When measuring the external male thread with a caliper, you will get a result in the range of 9.3–9.7 mm. For the internal female thread, the hole diameter is 8.5–8.9 mm, and a thread gauge will show 28 turns per inch.
What is the difference between 1/8" BSPT and 1/8" BSPP (G 1/8") thread?
BSPT thread (R 1/8") is a tapered thread and seals directly on the turns. BSPP thread (G 1/8") is a cylindrical (straight) thread and requires sealing on the face surface using a bonded seal (metal-rubber washer) or an O-ring.
Does a 1/8" BSPT thread fit a 1/8" NPT thread?
No. The BSPT thread has a 55° flank angle and a pitch of 28 turns per inch, while the NPT thread has a 60° angle and a 27 turns per inch pitch. Despite the similar diameter, they are not compatible, and joining them will lead to leakage.
How to seal a connection with a 1/8" BSPT thread?
To seal a connection with a 1/8" BSPT tapered thread, professional PTFE Teflon tape or liquid hydraulic thread sealants should be used.