Schematic cross-section of the male half, upper side only, with the centre line dashed and the open end on the left. Cone angles are drawn at their true angle from the axis; nothing else is to scale and no dimension should be measured off it. Thread shown: G 1/2 (14 TPI, 55 degree).
A deep, narrow cone - noticeably more pointed than a 37 degree flare. Common on Japanese equipment, usually with a loose female swivel nut.
Where it seals: Metal to metal, a 30 degree female seat against a 30 degree male cone.
Dimensions
Thread size, pitch and diameters for -08 JIS 30 (G 1/2).
Designation
-08 JIS 30 (G 1/2)
Thread
G 1/2 (14 TPI, 55 degree)
Threads per inch / pitch
14 TPI (1.814 mm pitch)
Basic major diameter (male)
20.95 mm / 0.825 in
Measured across the male crests
20.5 mm to 20.83 mm
Basic minor diameter (mating female)
18.63 mm / 0.734 in - computed from the 55 degree thread profile, not measured
Thread form
55 degree flank angle, parallel
Seat
30 degree flare cone or seat
How the size is named
Sized by BSPP trade size.
The thread is BSPP and gauges as BSPP. Only the 30 degree female cone tells this apart from a plain BSPP fitting, and a BSPP male with a bonded seal will screw into this and leak.
Working pressure
No working pressure is published for this connection. Ratings for it vary by manufacturer, body material, port form and seal, and no two independent sources in the register give the same figure under conditions they both state. A generic number here would be a decoration, not a rating. Read the pressure from the catalogue of the fitting you are actually installing.
A fitting with two different ends is only ever as strong as the weaker end, and any rating assumes the fitting is undamaged, correctly assembled and within its temperature range. Pressure ratings are safety-relevant: confirm them against the manufacturer specification before the system is charged.
What it mates with
A female G 1/2 (14 TPI, 55 degree) BSPP swivel nut with a 30 degree cone seat. It will thread onto a plain BSPP fitting and will not seal against it, because the seat angle is wrong.
Mating two different cone angles is the classic way to make a joint that holds pressure on the bench and weeps in service: the two cones touch on a line instead of a face, and tightening harder cold-flows the softer of the two rather than sealing it.
Do not mix these up
Fittings that measure like a -08 JIS 30 (G 1/2)
Every size below sits within 0.9 mm of this one across the male thread crests, which is inside what a worn or plated fitting and a hurried measurement produce together. Those marked same thread will screw together with this fitting.
Fittings in other standards whose male thread diameter is close to -08 JIS 30 (G 1/2).
This list is computed from the published diameters in the database rather than kept as a hand-written list, so a correction to a table can never leave a stale warning behind.
Answers
Common questions about -08 JIS 30 (G 1/2)
What thread is a -08 JIS 30 (G 1/2) fitting?
-08 JIS 30 (G 1/2) runs a G 1/2 (14 TPI, 55 degree) thread: 14 TPI (1.814 mm pitch), basic major diameter 20.95 mm / 0.825 in. Published identification charts read 20.5 mm to 20.83 mm across the male crests, which is the figure a caliper produces.
How do I tell a -08 JIS 30 (G 1/2) apart from a fitting that measures the same?
Look at the sealing surface. A deep, narrow cone - noticeably more pointed than a 37 degree flare. Common on Japanese equipment, usually with a loose female swivel nut. Metal to metal, a 30 degree female seat against a 30 degree male cone. The thread is parallel (straight) and the flank angle is 55 degrees.
What does a -08 JIS 30 (G 1/2) screw into?
A female G 1/2 (14 TPI, 55 degree) BSPP swivel nut with a 30 degree cone seat. It will thread onto a plain BSPP fitting and will not seal against it, because the seat angle is wrong.
What pressure is a -08 JIS 30 (G 1/2) rated for?
No working pressure is published here for this connection. Ratings vary by manufacturer, body material and seal, and no two independent sources in the register give the same figure under stated conditions for it. Read the rating from the catalogue of the fitting you are installing.
Dimensions are as defined by JIS B 0202, ISO 228-1. FittingKey is an independent reference and is not affiliated with, endorsed by or approved by any standards body or fitting manufacturer.
Every value on this page was checked against 3 independent published sources: