Hydraulic Thread Identification Guide
Ordering the wrong thread is the most common (and most avoidable) mistake in hydraulic purchasing. With a caliper, a thread pitch gauge, and this page, you can identify any common hydraulic connection in about two minutes.
Step 1 — Measure
Measure the thread outside diameter (male) or inside diameter (female) with a caliper, and the threads per inch (or millimeter pitch) with a pitch gauge. Then look at the sealing surface: is there a cone seat, an O-ring, or just threads?
Step 2 — Match the seat type
| Connection | Seat / seal | Thread form | Standard |
|---|---|---|---|
| JIC 37° flare | 37° cone seat, metal-to-metal | UN/UNF straight | SAE J514 |
| ORFS | O-ring in flat face groove | UN/UNF straight | SAE J1453 |
| SAE ORB port | O-ring at thread base, washer face | UN/UNF straight | SAE J1926-1 |
| NPT / NPTF | Tapered threads seal (dryseal on NPTF) | Tapered pipe | ASME B1.20.1 / SAE J476 |
| NPSM swivel | 30° internal seat | Straight pipe | SAE J514 |
| BSPP | Bonded washer or O-ring, parallel | Whitworth 55° straight | ISO 1179 |
| BSPT | Tapered threads seal | Whitworth 55° tapered | ISO 7-1 |
| Metric DIN 24° | 24° cone with ferrule or O-ring | Metric straight | DIN 2353 / ISO 8434-1 |
| SAE 4-bolt flange | O-ring face, split or captive flange | None (bolted) | SAE J518 |
Step 3 — Convert dash sizes
Hydraulic sizes use dash numbers: the dash is the nominal size in sixteenths of an inch. Our part numbers carry the dash size for each connection end.
| Dash | Nominal size | Dash | Nominal size |
|---|---|---|---|
| -02 | 1/8" | -12 | 3/4" |
| -04 | 1/4" | -16 | 1" |
| -05 | 5/16" | -20 | 1-1/4" |
| -06 | 3/8" | -24 | 1-1/2" |
| -08 | 1/2" | -32 | 2" |
| -10 | 5/8" | -40 / -48 | 2-1/2" / 3" |
Common JIC thread sizes
| Dash | Tube OD | Thread (UNF) |
|---|---|---|
| -04 | 1/4" | 7/16-20 |
| -06 | 3/8" | 9/16-18 |
| -08 | 1/2" | 3/4-16 |
| -10 | 5/8" | 7/8-14 |
| -12 | 3/4" | 1-1/16-12 |
| -16 | 1" | 1-5/16-12 |
| -20 | 1-1/4" | 1-5/8-12 |
| -24 | 1-1/2" | 1-7/8-12 |
Still not sure?
Take two photos — one straight on at the threads, one of the sealing face — note your caliper measurements, and send them to us. We identify mystery fittings for customers every week. If you have the old part's brand and number, the cross-reference desk is even faster.