Hydraulic Fitting Torque Chart
The SAE/ISO way to tighten a fitting is the flats-from-finger-tight method — hand-tight, then a set number of hex flats. It gives the right clamp load without a torque wrench, and it's far more forgiving than chasing a torque number.
Why flats, not just torque
The most common cause of leaks is over-tightening
On a flare fitting, the seal is metal-to-metal on the cone — crank it too hard and you crack the flare, which makes the leak permanent. The flats method sidesteps that: it controls how far the nut turns rather than how hard you pull, so plating, oil and surface finish don't throw the result off. That's why SAE and ISO base flare and flareless assembly on flats from finger tight.
The method
Flats from finger tight (FFFT)
- Hand-tighten the nut until you feel firm wrench resistance — roughly 30 in-lb (about 3.4 Nm). The sealing surfaces are now seated.
- Mark a line across one flat of the nut and continue it onto the body, so you can see exactly how far the nut turns.
- Turn the nut the number of flats for that connection (one flat = one hex face = 1/6 of a turn).
- Hold the body with a second wrench so it can't rotate while you turn the nut.
- Re-mark the final position — it doubles as a quick check later that nothing has backed off.
By connection type
How tight, by connection
The rule of thumb: flare and flareless connections are set by flats. O-ring–sealed ports (ORB, ORFS, BSPP) need a torque wrench to the manufacturer's seated value, because the O-ring needs controlled compression.
| Connection | Standard | Method | From finger / wrench tight |
|---|---|---|---|
| JIC 37° flare — tube nut | SAE J514 · ISO 8434-2 | flats | 2 flats (1/3 turn) |
| JIC 37° flare — swivel / hose end | SAE J514 · ISO 8434-2 | flats | 1½ flats (1/4 turn) |
| SAE 45° flare | SAE J512 | flats | ~2 flats (low pressure) |
| Flareless / DIN 24° bite-type | ISO 8434-1 (DIN 2353) | turns | Pre-set the ferrule (~1½ turns), then final tighten per the manufacturer |
| O-ring face seal (ORFS) | SAE J1453 | flats | Seat the faces square, then flats per the manufacturer's chart |
| O-ring boss / straight thread (ORB) | SAE J1926 | torque | Torque wrench to the manufacturer's seated value |
| BSPP port (bonded washer / soft seal) | ISO 1179 | torque | Torque wrench to the manufacturer's seated value |
| Tapered pipe (NPT / BSPT) | ANSI/ASME B1.20.1 | turns | Thread sealant, then ~2–3 turns past hand tight |
These are general assembly values to the standards listed. Smaller sizes generally need a little more rotation than larger ones, and exact flats or torque vary by fitting manufacturer, material and plating — always follow the fitting manufacturer's published procedure where one is given, and confirm the joint holds under operating pressure. Don't use thread sealant on flare (JIC / SAE 45°) or O-ring seals; it isn't needed and can prevent proper seating.
Keep going