Dimensions
| Designation | 1/8-28 BSPP |
|---|---|
| Major (outside) diameter | 9.728 mm · 0.383" |
| Pitch | 0.907 mm · 28 TPI |
| Pitch diameter | 9.139 mm · 0.3598" |
| Minor diameter (external) | 8.615 mm · 0.3392" |
| Minor diameter (internal) | 8.746 mm · 0.3443" |
| Recommended tap drill | - |
BSPP (G) - British parallel pipe
1/8-28 BSPP
1/8-28 BSPP pipe thread: 28 TPI, major Ø 9.728 mm.
Tap drill
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9.728 mm major Ø
Profile
Thread form & key diameters
Tightening torque estimate
Pipe threads are made up to a seal against the mating flanks, not tightened to a bolt preload, so no proof load or tightening-torque figure applies.
Put 1/8-28 BSPP on a job sheet
The bolt schedule collects the fasteners for one job onto a single sheet - tap drill, wrench size, grade and tightening torque on every line, taken straight from pages like this one. Free schedules hold 3 lines and are saved in this browser only.
What tap drill do I need for 1/8-28 BSPP?
1/8-28 BSPP is a BSPP pipe thread running at 28 threads per inch on a 9.728 mm major diameter. BSPP (G) is a parallel thread sealed by a bonded washer or gasket, not by thread interference - so it has no tapered tap-drill sizing.
All values are generated from the standard thread formulas (ISO 68-1 / ASME B1.1) and published standard tables - not hand-entered. See the full reference.
Frequently asked questions
What drill size do I need to tap 1/8-28 BSPP?
Drill - before tapping 1/8-28 BSPP. BSPP (G) is a parallel thread sealed by a bonded washer or gasket, not by thread interference - so it has no tapered tap-drill sizing.
Is 1/8-28 BSPP a tapered or parallel thread?
1/8-28 BSPP is parallel. BSPP (G) threads do not seal on the thread itself; the joint seals on a bonded washer, gasket or O-ring at the face.
How many threads per inch does 1/8-28 BSPP have?
1/8-28 BSPP runs at 28 threads per inch, a pitch of 0.907 mm, on a major diameter of 9.728 mm.
Is there a torque spec for 1/8-28 BSPP?
No. Pipe threads are made up to a seal against the mating flanks, not tightened to a bolt preload, so no proof load or tightening-torque figure applies.
Same diameter
Other 1/8" BSPP threads
The pipe this thread runs on
NPS 1/8 pipe
NPS 1/8 pipe is 0.405 in across the outside whatever the schedule; at standard wall (std) the wall is 0.068 in and the bore 0.269 in.
Schedule 10ID 0.307"Schedule 30ID 0.291"Schedule 40ID 0.269"Schedule 80ID 0.215"Standard wall (STD)ID 0.269"Extra strong (XS)ID 0.215"
Full dimensions for the standard wall · every schedule in the chart
Nearby sizes