JIC and UNF Thread Size Chart

JIC 37° (SAE J514 / ISO 8434-2) and SAE O-ring boss (ORB, SAE J1926 / ISO 11926) connections use the same UN/UNF threads. For each dash size from -2 to -32, the chart gives the tube OD, thread, pitch, nominal and typical measured major diameter, and the basic minor diameter of the female thread.

How to read dash sizes

The dash number gives the tube OD in sixteenths of an inch: -6 = 6/16" = 3/8" tube (9.53 mm), -8 = 1/2" tube (12.7 mm). Each dash size has a single thread: 7/16-20 UNF for -4, 3/4-16 UNF for -8, 1-5/16-12 UN for -16. From -12 upward, the thread is from the 12 TPI constant-pitch UN series. On hose, however, the dash number indicates the inside diameter; a -8 hose has a 1/2" ID and is usually used with a -8 JIC end, although this is not mandatory.

Chart columns

• Nominal OD is the basic size of the thread (19.05 mm for 3/4-16 UNF).
• Typical reading range is the value to expect with a caliper on a male thread; because of tolerances it can be 0.3–0.45 mm below nominal (18.65–19.05 mm for -8).
• Female basic minor diameter is calculated from the basic thread profile; the value actually measured on a female thread is slightly larger.

JIC vs ORB

JIC seals by metal-to-metal contact between the 37° cone of the male end and the 37° seat of the female end; the thread only provides the clamping force. On ORB, the male end seats in the port with an O-ring under the hex; the O-ring is compressed into the chamfer at the port mouth. ORB O-rings are from the AS568 9xx series, and the number gives the tube OD in sixteenths of an inch: 904 for -4, 908 for -8, 916 for -16.

Don't mix up 37° and 45°

SAE 45° flare connections, found on refrigeration and low-pressure lines, use the same thread as JIC in sizes -2, -3, -4, -5, -8 and -10. The nut screws on, but the cones don't seat fully and the joint leaks. The thread chart can't tell the two apart; check the cone angle with a gauge.

JIC, ORFS and metric threads

ORFS threads differ from the JIC thread of the same dash size (at -8, ORFS is 13/16-16 and JIC is 3/4-16). On the other hand, the same thread corresponds to different dash sizes in the two systems: 9/16-18 UNF is both JIC -6 and ORFS -4, and 1-3/16-12 UN is both JIC -14 and ORFS -12. Metric threads come close as well: between 1-1/16-12 UN (26.988 mm) and M27×2 the diameter difference is only 0.013 mm, and between 5/16-24 UNF (7.938 mm) and M8×1 it is 0.062 mm. Pitch separates these pairs: 2.117 vs 2.0 mm, and 1.058 vs 1.0 mm.

On stainless steel JIC connections

Scratches and dents on the 37° cone face turn directly into leaks; protect disassembled parts with caps. Overtightening crushes the cone and causes galling on stainless threads; tighten to the torque or number of turns in the manufacturer's instructions. The -14 size is defined in the standard but rarely used in the market; confirm the tube size when looking for spare parts.