1/4" BSPT Thread
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1/4" BSPT thread (R 1/4") – British tapered thread in hydraulics and pneumatics
1/4" BSPT thread (short for British Standard Pipe Tapered, designation R 1/4" for the male tapered external thread and Rc 1/4" for the female internal thread) is a standardized British tapered pipe thread with a Whitworth profile according to ISO 7-1, DIN 2999, BS 21, and EN 10226 [1]. It is commonly used in power hydraulic systems, industrial pneumatics, gas installations, measuring equipment, and machine construction [1]. It features a tapered profile with a 1:16 (6.25%) taper and a 55° thread angle. The connection is sealed directly on the thread turns by mechanically pressing the male cone (R 1/4") into the tapered seat (Rc 1/4") or cylindrical seat (G 1/4" / Rp 1/4"). For the 1/4" BSPT size, the thread pitch is 19 turns per inch (19 TPI / pitch \~1.337 mm) [1]. The outer diameter of the male thread measured with a caliper is between 12.9 mm and 13.1 mm, while the internal diameter of the female thread is between 11.4 mm and 11.9 mm [1]. The 1/4" BSPT thread is a common connection standard in pumps, valves, actuators, manifolds, and machine connectors of European and Asian manufacture [1].
Application and technical characteristics of the 1/4" BSPT thread
Fastening components, adapters, and crimped ends with 1/4" BSPT (AGR-K / C31) thread are used in pressure circuits where a reliable, self-sealing threaded connection resistant to high pressure, vibration, and operating temperature spikes is required [1, 2].
- Tapered sealing profile (1:16 taper): Enables sealing directly on the thread turns using PTFE tape, hemp, or liquid anaerobic sealant.
- British Whitworth thread angle of 55°: A standard characteristic of European pipe threads, distinguishing it from the American 1/4" NPT tapered thread (where the angle is 60° and the pitch is 18 TPI) [1].
- Precise caliper measurement dimensions: The male thread's outer diameter is 12.9–13.1 mm, and the female thread's diameter is 11.4–11.9 mm with a pitch of 19 turns per inch [1].
- Wide compatibility in pressure installations: Commonly used in shut-off valve bodies, manifold blocks, pressure gauges, hydraulic units, and pneumatic installations [1].
- Wide selection of fittings and adapters: The offer includes straight fittings, elbows, tees, reducers, and hose ends (AGR-K) with a 1/4" BSPT thread [1, 2].
Why choose 1/4" BSPT thread components at the HYDRON store?
All fittings, adapters, and ends with 1/4" BSPT thread offered by the HYDRON store are manufactured in accordance with strict ISO 9001 quality standards from free-cutting steel protected against corrosion with a zinc coating and from AISI 316L stainless steel [3]. Correct identification of the thread with a caliper is essential in workshop practice – confusing the 1/4" BSPT tapered thread with the American 1/4" NPT thread (difference in pitch 19 TPI vs 18 TPI and angle 55° vs 60°) leads to loss of tightness and destruction of the thread [1]. Furthermore, distinguishing BSPT (tapered) from BSPP (cylindrical G 1/4") allows for choosing the correct sealing method [1]. 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 lines, matching AGR-K hose ends, durable hydraulic quick couplers and extensive hydraulic directional control valves [1, 2, 4].
Technical specification
Technical parameter | Value / Description |
|---|---|
Thread designation | 1/4" BSPT / R 1/4" (male tapered) / Rc 1/4" (female tapered) [1] |
Manufacturing standards | ISO 7-1, BS 21, DIN 2999, EN 10226 [1] |
Male thread outer diameter (caliper) | 12.9 mm – 13.1 mm [1] |
Female thread inner diameter (caliper) | 11.4 mm – 11.9 mm [1] |
Thread pitch (number of turns per inch) | 19 turns per inch (19 TPI / pitch \~1.337 mm) [1] |
Thread angle and taper | 55° Angle (Whitworth), 1:16 taper (6.25% convergence) [1] |
Sealing method | Sealing on the thread using PTFE tape, hemp, or liquid anaerobic glue |
Available materials and coating | Free-cutting/forged galvanized steel, AISI 316L stainless steel, brass [3] |
Frequently Asked Questions (FAQ)
How to measure a 1/4" BSPT thread with a caliper?
When measuring the external male thread with a caliper, you will get a result in the range of 12.9–13.1 mm. For the internal female thread, the hole diameter is 11.4–11.9 mm, and the thread gauge will show 19 turns per inch [1].
What is the difference between 1/4" BSPT thread and 1/4" BSPP (G 1/4") thread?
BSPT thread (R 1/4") is a tapered thread and seals directly on the turns. BSPP thread (G 1/4") is a cylindrical (straight) thread and requires sealing on the face using a bonded seal or an O-ring [1].
Does a 1/4" BSPT thread fit a 1/4" NPT thread?
No. BSPT thread has a 55° thread angle and a pitch of 19 turns per inch, while NPT thread has a 60° angle and a pitch of 18 turns per inch. Despite a similar diameter, they are not compatible, and connecting them will lead to leakage [1].
How to seal a 1/4" BSPT threaded connection?
To seal a connection with a 1/4" BSPT tapered thread, professional PTFE Teflon tape, hemp with sealing paste, or liquid hydraulic thread sealants should be used.