Can you use brass or hardware-store fittings on hydraulics?
Only if the fitting has a published working pressure at or above your machine’s maximum. The material isn’t the test: brass hydraulic adapters exist and are rated lower than steel, and a fitting with no published rating doesn’t qualify, whatever it’s made of.
The rule: a published pressure rating
The published maximum working pressure of every hose, tube and fitting must be equal to or greater than the system’s maximum pressure. A hose assembly’s own rating is the lowest of its parts’ ratings, so one under-rated adapter sets the limit for the whole line.
Brass hydraulic fittings exist
Parker’s Triple-Lok (JIC 37°) tube fittings come as standard in steel, stainless steel, brass and aluminum, and each material has its own rating. Its 6-8 F5OX, the adapter from a -8 ORB port to a -6 JIC hose, is rated 6,000 psi in steel, 7,200 psi in stainless steel and 3,300 psi in brass. Parker’s torque for brass fittings is 65% of its value for steel.
So a brass part made and rated for hydraulics can be the right part, if its rating covers your machine. The same part in steel has more margin.
Hardware-store plumbing fittings
Hardware stores sell many fittings with the same thread names as hydraulic ones, such as NPT and BSP, made for water, gas or air. One of them belongs on a hydraulic line only if its maker publishes a working pressure at or above your machine’s maximum. If you can’t find a published rating for it, don’t put it on the machine.
Getting a rated part
Parker prints the working pressure of each of its parts in its catalog, so look up the rating of the exact part. Name the part by its two ends first: the hydraulic adapter finder does that from the port and the hose end.
Before you loosen a fitting
Turn the machine off, put the equipment in a safe, neutral position and release the pressure before you loosen anything. Turning off the pump may not release it: check valves can hold pressure in a hose, and it can take minutes or hours to bleed away.
Never feel for a leak with your hand or any other part of your body. Oil under pressure can go through skin, and a pinhole leak can be almost invisible.
If oil gets under your skin, get medical help at once, even if it doesn’t hurt. An injection injury can lead to amputation.
Threads that screw together don’t prove the parts match. Some parts that don’t belong together still thread on, and then leak or come apart under pressure.
Use only fittings whose published working pressure is at or above your machine’s maximum pressure. If a fitting has no published rating, don’t use it.
Stay clear the first time you run the machine under pressure after a repair.
Common questions
Is brass OK for hydraulic fittings?
It can be, if the brass fitting is made and rated for the pressure. Parker's brass adapters are rated lower than its steel ones: the 6-8 F5OX is 3,300 psi in brass and 6,000 psi in steel.
Can I use a plumbing fitting on a tractor or log splitter?
Only if its maker publishes a working pressure at or above the machine's maximum pressure. Without a published rating, don't.
Which part of a hose assembly sets its pressure rating?
The lowest-rated one: an assembly's maximum working pressure is the lower of the published ratings of its hose, tube and fittings.
The pressure rule comes from Parker’s hose and fitting safety guide, the brass ratings and torque from Parker’s fitting catalogs, and the safety lines from Parker, Gates and the UK Health and Safety Executive. Checked against published data from Parker Hannifin, Gates and UK Health and Safety Executive.
See all 7 sources
Parker Hannifin, Catalog 4300, Tube Fittings (PDF Version 13, 8/2026): straight thread, pipe thread and BSPP adapters and their part numbers (pp. A14-A15, B15-B19, E15, E17), port connection guidelines (p. E5), JIS fittings (p. G3), K4 vs JIS 60° cones (p. H4), Komatsu style 30° flare (p. I3), brass Triple-Lok ratings (pp. B7, B15)
Parker Hannifin, Catalog 4400, Hose, Fittings, and Equipment (October 9, 2026), Hydraulic Technical Section pp. 456-473: identifying fitting types and sealing methods, measuring threads with a gauge and caliper, thread tables for NPTF, JIC 37°, SAE 45°, O-ring boss, ORFS, BSPP, BSPT, metric DIN 24° and JIS 30°; hose dash sizes (p. 6)
Parker Hannifin, Parker Safety Guide for Selecting and Using Hose, Tubing, Fittings, Connectors, Conductors, Valves and Related Accessories, Publication 4400-B.1, revision B (8-NOV-2024), in Catalog 4400 pp. 495-498: published maximum working pressure at or above the system's (2.2), never feel for a leak, pressure that stays after shutdown, injection injuries (5.6)
Gates, Safe Hydraulics Pocket Guide: tools for coupling identification, inspection steps (turn off and lock out the power, put the equipment in a safe and/or neutral position), components that thread together but aren't compatible
Gates, Hydraulic Hoses & Couplings Product & Application Guide (2024): avoid fluid injection injuries, get medical help at once even if no pain is felt, stay out of hazardous areas while testing under pressure
UK Health and Safety Executive, High pressure fluid injection hazards (agriculture, machinery): injection injuries, operator errors such as searching for leaks with bare hands and failing to release pressure
UK Health and Safety Executive, Safety alert: Hydraulic injection injury: injuries at low pressures, prompt medical treatment, replacement fittings matched to the original equipment maker's specification
General guidance from fitting makers' catalogs and safety guides, not a substitute for your machine's manual. Release the pressure before you loosen any fitting, use only parts rated for your machine's pressure, and if you can't identify a fitting for sure, take it to a hydraulic hose shop.