- Metric hydraulic adapter fittings resemble British and SAE (American) fittings in many ways.
- One of the most popular Metric fitting styles is the ISO 9974. ISO 9974 fittings are commonly used in hydraulic port applications. ISO 9974 fittings resemble SAE O-ring boss fittings and British Standard Parallel Pipe (BSPP) ISO 1179 fittings, the difference being metric threads. ISO 9974 fittings use a captive or retained seal at the base of the threads that mates to a seat surface on the female fitting or ported surface on a hydraulic cylinder or valve.
- Metric port fittings ISO 6149 also are very similar to ISO 9974 port fittings except they use a non-retained O-ring same as the SAE O-ring Boss Fittings.
- Another popular Metric fitting series is the DIN tube fittings. DIN tube fittings have a 24° chamfered seat on the inside of the male fitting that identifies the fitting as DIN, that 24° seat is where the seal takes place when joining a DIN male to a DIN female fitting. DIN fittings employ an identification system used by most manufacturers, this system combines the tube O.D. size and the tube Series, for example, a fitting that is 8mm and heavy duty would be marked “S08”.
LL = Extra Light Duty
L = Light Duty
S= Heavy Duty
- Metric threads are called out using the distance between two threads as the Thread Pitch, this is different than American SAE and British Standard threads that are designated by Threads per Inch.
There are three common thread pitches used on all Metric DIN fittings, 1.0mm, 1.5mm & 2.0mm pitches.