Hydraulics & Fluid Power Reference Library · Wall Charts

Seat Angle Identification Chart

How to tell 37°, 45°, 24°, 30° and 60° fitting seats apart with a seat angle gauge, and which thread families go with each seat.

Ref HY-0056SAE J514SAE J512ISO 8434-1

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Many hydraulic fittings seal metal-to-metal on a seat: a cone or flare where the male and female meet. The seat angle must match exactly. A 37° male in a 45° female touches on a thin line and leaks. Several families share thread sizes, so the seat angle is often the only way to tell them apart.

How to identify

Clean the seat completely.
Use a seat angle gauge made for fitting identification.
On a male fitting, set the gauge on the cone nose. On a female, set it inside the flare or cone.
The correct blade sits flat with no light showing between gauge and seat.
Read the angle as the gauge kit labels it. Trade names mix angles measured from the centerline and included angles, so use the gauge rather than a protractor.
Then measure the thread to confirm the family.

Seat angle chart

Seat as named in the trade	Common family	Thread used with it	Typical use
37° flare	JIC (SAE J514)	UN/UNF	North American hydraulic hose and tube
45° flare	SAE 45° (SAE J512)	UNF	Refrigeration, fuel, low pressure lines
24° cone	Metric DIN (ISO 8434-1)	Metric fine	European equipment; cutting ring or O-ring cone
30° flare	JIS (Japanese)	BSPP or metric	Japanese-built equipment
60° cone	BSPP hose ends, some metric and NPSM swivels	BSPP, metric or NPSM	European and Asian hose ends

Key points

37° and 45° look close and share several thread sizes. Gauge every one you are unsure of.
JIS 30° and BSP 60° cone are easy to confuse. Confirm the thread and the equipment origin.
Some 24° fittings use an O-ring in the cone (often called DKO). Others use a cutting ring. They mate with the same 24° body but are different hose ends.
A damaged, scratched or flattened seat will not seal at any angle. Replace it.

Common mistakes

Identifying the fitting by thread alone.
Guessing the angle by eye.
Fitting an O-ring cone (DKO) end into a 24° body that still holds an old cutting ring.

Governing standards: SAE J514 (37° flare); SAE J512 (45° flare); ISO 8434-1 (24° cone); ISO 8434-2 (37° flare); fitting maker identification guides.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

More in Wall Charts

← All Hydraulics & Fluid Power sheets