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: 3/4-16 UNF.
A male nose machined to a shallow cone, or a female fitting with a coned recess. Measured off the fitting axis the cone half-angle is 37 degrees, so the included angle across the cone is 74 degrees.
Where it seals: Metal to metal, cone against the flared tube or the mating cone. No O-ring, no sealant.
Dimensions
Thread size, pitch and diameters for -08 JIC.
Designation
-08 JIC
Thread
3/4-16 UNF
Threads per inch / pitch
16 TPI (1.587 mm pitch)
Basic major diameter (male)
19.05 mm / 0.75 in
Measured across the male crests
18.9 mm to 19.1 mm
Basic minor diameter (mating female)
17.33 mm / 0.682 in - computed from the 60 degree thread profile, not measured
Thread form
60 degree flank angle, parallel
Seat
37 degree flare cone
Tube outside diameter
0.5 in (12.7 mm)
How the size is named
Sized by dash number, which is the tube outside diameter in sixteenths of an inch: -08 is 8/16 in, half-inch tube.
Working pressure
Published working pressure4,500 psi (310 bar)
This figure applies only under these conditions: Steel fitting, rigid 37 degree flare end, at a 4 to 1 design factor against minimum burst per SAE J514. Adjustable and swivel ends of the same size are rated lower. A fitting with two different ends takes the lower of the two ratings. Brass, stainless and any manufacturer's own uprated part carry different figures - read them from that 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 female 3/4-16 UNF swivel or port with a 37 degree cone seat, on the same dash size. The joint seals metal to metal on the cone, so no tape, no sealant and no O-ring belong anywhere in it.
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 JIC
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 JIC.
Same thread - it will screw together and the seal will be wrong
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 JIC
What thread is a -08 JIC fitting?
-08 JIC runs a 3/4-16 UNF thread: 16 TPI (1.587 mm pitch), basic major diameter 19.05 mm / 0.75 in. Published identification charts read 18.9 mm to 19.1 mm across the male crests, which is the figure a caliper produces.
How do I tell a -08 JIC apart from a fitting that measures the same?
Look at the sealing surface. A male nose machined to a shallow cone, or a female fitting with a coned recess. Measured off the fitting axis the cone half-angle is 37 degrees, so the included angle across the cone is 74 degrees. Metal to metal, cone against the flared tube or the mating cone. No O-ring, no sealant. The thread is parallel (straight) and the flank angle is 60 degrees.
What does a -08 JIC screw into?
A female 3/4-16 UNF swivel or port with a 37 degree cone seat, on the same dash size. The joint seals metal to metal on the cone, so no tape, no sealant and no O-ring belong anywhere in it.
What pressure is a -08 JIC rated for?
4,500 psi (310 bar). Steel fitting, rigid 37 degree flare end, at a 4 to 1 design factor against minimum burst per SAE J514. Adjustable and swivel ends of the same size are rated lower. A fitting with two different ends takes the lower of the two ratings. Brass, stainless and any manufacturer's own uprated part carry different figures - read them from that maker's catalogue.
Dimensions are as defined by SAE J514, ISO 8434-2. 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 7 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, gageref-jic
Four publishers give the same dash-to-tube-size map. Three of them carry the -14 row; one omits it.
Thread designation and pitch
tompkins, mcgill-id, chs-orfs, gageref-jic
All four give the same thread for every dash size, including the 12 TPI constant-pitch series from -12 upward.
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, apex-threadid, mcgill-id
Three identification charts. Their figures sit within 0.25 mm of one another, and the span of all three is what the size page publishes.
Working pressure
tompkins, brennan-pressure
Two manufacturer catalogues, both stating a steel fitting at a 4 to 1 design factor against minimum burst per SAE J514. They agree on all thirteen sizes to the psi.