SAE J512 · SAE J533
A straight Unified inch thread with a 45 degree metal cone seat. Shares its thread with JIC at several sizes, which is the single most common mis-identification in the trade.
8 sizes60 degree flanksParallel thread45 degree flare cone
The same shape as a 37 degree flare but visibly blunter - a wider, shorter cone. Side by side the difference is obvious; alone it is not.
Where it seals: Metal to metal, cone against the flared tube. No O-ring, no sealant.
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.
Sized by tube outside diameter in inches rather than by dash number.
Where you will find it: Automotive fuel and brake lines, refrigeration, gas and low pressure fluid lines. Not a high pressure hydraulic connection.
Also searched as: SAE 45, 45 degree flare, flare fitting, SAE flare.
All sizes
| Size | Thread | TPI / pitch | Basic major Ø | Measured across crests | Tube / trade size | Working pressure |
|---|---|---|---|---|---|---|
| 1/8 in SAE 45 | 5/16-24 UNF | 24 TPI (1.058 mm pitch) | 7.94 mm / 0.313 in | Not published | 0.125 in | Manufacturer-specific |
| 3/16 in SAE 45 | 3/8-24 UNF | 24 TPI (1.058 mm pitch) | 9.53 mm / 0.375 in | Not published | 0.1875 in | Manufacturer-specific |
| 1/4 in SAE 45 | 7/16-20 UNF | 20 TPI (1.27 mm pitch) | 11.11 mm / 0.438 in | 11 mm to 11.18 mm | 0.25 in | Manufacturer-specific |
| 5/16 in SAE 45 | 1/2-20 UNF | 20 TPI (1.27 mm pitch) | 12.7 mm / 0.5 in | 12.5 mm to 12.7 mm | 0.3125 in | Manufacturer-specific |
| 3/8 in SAE 45 | 5/8-18 UNF | 18 TPI (1.411 mm pitch) | 15.88 mm / 0.625 in | 15.9 mm to 16 mm | 0.375 in | Manufacturer-specific |
| 1/2 in SAE 45 | 3/4-16 UNF | 16 TPI (1.587 mm pitch) | 19.05 mm / 0.75 in | 19.05 mm to 19.1 mm | 0.5 in | Manufacturer-specific |
| 5/8 in SAE 45 | 7/8-14 UNF | 14 TPI (1.814 mm pitch) | 22.23 mm / 0.875 in | 22.1 mm to 22.35 mm | 0.625 in | Manufacturer-specific |
| 3/4 in SAE 45 | 1 1/16-14 UNF | 14 TPI (1.814 mm pitch) | 26.99 mm / 1.063 in | 26.9 mm to 26.92 mm | 0.75 in | Manufacturer-specific |
No working pressure is published for this standard. No two independent sources in the register give the same figure under conditions they both state, and a generic number would be a decoration rather than a rating. Read it from the manufacturer's catalogue.
On paper
Dimensions are as defined by SAE J512, SAE J533. 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:
| Column | Sources | What they gave |
|---|---|---|
| Dash and trade size | ryco-sae, mcgill-id, gates-idchart | Three publishers agree on the eight sizes carried here. One extends the series to -14 and -16; those two are recorded as gaps. |
| Basic major diameter | ryco-sae, 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, for the six sizes both carry. |
| Working pressure | ryco-sae, mcgill-id | Neither publisher gives a working pressure for this connection, so none is published. Ratings are per part, from the maker's catalogue. |