Fitting Thread Size Reference

Common Terms

Under Head Length-AN/JIC (SAE 37 )
Distance from under hex to end of fitting or flair- important when threading into (female) ports so the fitting does not “bottom” on the hex prior to contacting the flair sealing surface.

Seals on Thread
Taper contact seal with sealant or tape (NPT).

Seals on Flair
Using one of each (concave & convex) flair to seal- angle may vary, but needs to be consistent between both sealing surfaces.

Convex
Male flair seals common on -AN (male) and some metric (male) unions and some threaded ports. Convex male > seals on > Concave female

Concave
Female flair seal common on -AN hose ends, most metric (male) unions and some threaded ports. Concave male < seals on < Convex female

Flat
No sealing surface; use crush-washer under hex head.

Inverted Flair (or reverse flair)
A term used in place of concave and convex, but always refers to- concave on male and convex on female.

Globe Seal
BSP & Metric (female) hose ends- use a radius sealing surface designed seal on a range of fixed angles.

Types of Fittings

-AN/JIC (SAE 37)

O-Ring Boss (ORB)

Dash sizes are the numerators of fractions with a denominator of 16. For example, -08 is equal to 8⁄16 which is equal to 1⁄2. ORB version is similar thread but seals with o-ring rather than flair. SAE 45 seals on 45 degree flair and is similar in thread to SAE 37 (except -12 which is 14tpi). SAE45 is commonly used in automotive a/c plumbing.

National Pipe Tapered (NPT)

NPT or NPTF is a popular American thread type often referred to as “pipe thread”. NPT fittings are designed to seal with some thread deformation and use of teflon liquid or tape. The nominal pipe size can be identified by physically measuring the thread diameter, then subtracting 1/4″.

British Standard Pipe (BSP)

Very common British thread. The female could also have a 60 degree convex seat instead of globeseal. To accurately identify any BSPP or BSPT fitting, measure from one side of the thread to the other and refer to the chart.

*How do I know what size I have?
The nominal pipe size can be identified by physically measuring the thread diameter, then subtracting ¼″

Dash Size

Tube O.D.

1/8

3/16

1/4

5/16

3/8

7/16

1/2

5/8

3/4

7/8

1¼

1½

Hose I.D.

1/8

3/16

1/4

5/16

3/8

1/2

5/8

3/4

1¼

1½

SAE O-Ring Thread

5/16 - 24

3/8 - 24

7/16 - 20

1/2 - 20

9/16 - 18

3/4 - 16

7/8 - 14

11/16 - 12

13/16 - 12

15/16 - 12

15/8 - 12

17/8 - 12

NPTF Pipe Thread

1/8-27

1/4-18

3/8-18

1/2-14

3/4-14

1-11½

1¼-11½

1½-11½

BSPP / BSPT

1/8-28

1/4-19

3/8-19

1/2-14

3/4-14

1-11

1¼-11

1½-11

SAE 45-Flare Thread

5/16-24

3/8-24

7/16-20

1/2-20

5/8-18

11/16-24

3/4-16

7/8-14

11/16-14

Inverted Flare Thread

5/16-24

3/8-24

7/16-20

1/2-20

5/8-18

11/16-24

3/4-16

7/8-14

11/16-14

Compression Thread

5/16-24

3/8-24

7/16-20

1/2-20

9/16-18

3/4-16

1-12

1½-12

15/16-12

17/8-12

2½-12

Metric Thread

M10x1.0

M12x1.5

M14x1.5

M16x1.5

M18x1.5

M20x1.5

M22x1.5

M24x1.5

M26x1.5

M27x2.0

M30x2.0

M33x2.0

M36x2.0