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: 1 7/8-12 UN.
A straight male thread with a plain unthreaded shoulder behind it carrying an O-ring, screwing into a port with a flat spotface at the top of the threads.
Where it seals: The O-ring squashed between the fitting shoulder and the machined spotface of the port. The thread only holds the load.
Dimensions
Thread size, pitch and diameters for -24 SAE ORB.
Designation
-24 SAE ORB
Thread
1 7/8-12 UN
Threads per inch / pitch
12 TPI (2.117 mm pitch)
Basic major diameter (male)
47.62 mm / 1.875 in
Measured across the male crests
47.6 mm to 47.75 mm
Basic minor diameter (mating female)
45.33 mm / 1.785 in - computed from the 60 degree thread profile, not measured
Thread form
60 degree flank angle, parallel
Seat
O-ring boss (straight thread port)
Tube outside diameter
1.5 in (38.1 mm)
O-ring
AS568-924
How the size is named
Sized by dash number. The thread is identical to the JIC thread of the same dash - only the sealing end differs.
Working pressure
Published working pressure1,500 to 2,000 psi (103 to 138 bar)
This figure applies only under these conditions: Steel stud in a steel port, at a 4 to 1 design factor against minimum burst per SAE J514. The higher figure is a straight (non-adjustable) stud, the lower an adjustable stud with lock nut and washer. Both publishers give the same pair. Brass, stainless and uprated proprietary parts differ - read the maker's catalogue.
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 straight-thread port machined to 1 7/8-12 UN with a flat spotface at the top of the threads. The O-ring on the fitting shoulder is the seal; the thread carries the load only.
The O-ring is the seal, not the thread. Running an O-ring boss fitting into a tapered port, or torquing it down without the O-ring seated against the spotface, damages the port face and the port is then scrap.
Do not mix these up
Fittings that measure like a -24 SAE ORB
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 -24 SAE ORB.
No - 0.64 mm apart on diameter, and a different pitch
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 -24 SAE ORB
What thread is a -24 SAE ORB fitting?
-24 SAE ORB runs a 1 7/8-12 UN thread: 12 TPI (2.117 mm pitch), basic major diameter 47.62 mm / 1.875 in. Published identification charts read 47.6 mm to 47.75 mm across the male crests, which is the figure a caliper produces.
How do I tell a -24 SAE ORB apart from a fitting that measures the same?
Look at the sealing surface. A straight male thread with a plain unthreaded shoulder behind it carrying an O-ring, screwing into a port with a flat spotface at the top of the threads. The O-ring squashed between the fitting shoulder and the machined spotface of the port. The thread only holds the load. The thread is parallel (straight) and the flank angle is 60 degrees.
What does a -24 SAE ORB screw into?
A straight-thread port machined to 1 7/8-12 UN with a flat spotface at the top of the threads. The O-ring on the fitting shoulder is the seal; the thread carries the load only.
What pressure is a -24 SAE ORB rated for?
1,500 to 2,000 psi (103 to 138 bar). Steel stud in a steel port, at a 4 to 1 design factor against minimum burst per SAE J514. The higher figure is a straight (non-adjustable) stud, the lower an adjustable stud with lock nut and washer. Both publishers give the same pair. Brass, stainless and uprated proprietary parts differ - read the maker's catalogue.
What size O-ring does a -24 SAE ORB take?
AS568-924. The O-ring is the seal on this connection - the thread only carries the load - so a missing, pinched or wrong-size ring leaks no matter how hard the joint is pulled up.
Dimensions are as defined by SAE J1926-1, ISO 11926-1. 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 6 independent published sources:
Which published source supplied each column, and what it gave.
Column
Sources
What they gave
Dash and trade size
tompkins, mcgill-id, chs-orfs, gates-idchart
Four publishers, same dash-to-port-size map, and all four give the ORB thread as identical to the JIC thread of the same dash.
Basic major diameter
tompkins, mcgill-id
The thread designation fixes the basic major diameter: a 3/4-16 UNF thread has a basic major diameter of 0.750 in, which is 19.05 mm at 1 in = 25.4 mm exactly. The inch and millimetre columns are that one figure in two units.
Measured male thread diameter
gates-idchart, mcgill-id
Two identification charts, within 0.25 mm at every size.
O-ring size
globaloring, gates-idchart
The AS568 900-series dash number comes from the O-ring maker's table, indexed by nominal port size. It was cross-checked against the measured O-ring inside diameters printed on the coupling chart: all thirteen agree to within 0.1 mm.
Working pressure
tompkins, brennan-pressure
Two catalogues, steel, 4 to 1 against minimum burst per SAE J514, each giving a separate figure for a straight stud and for an adjustable stud. Both pairs match on all thirteen sizes.