Guides · 5 articles · free
The size pages tell you what a fitting measures. These guides cover the things a table cannot: how to take the measurement, what the number on the part actually names, why a joint that was pulled up hard still weeps, and what a pressure rating is a rating for. Every figure quoted links back to the size page it came from.
8 min read
The four measurements that identify a hydraulic fitting, in the order to take them: thread diameter with a caliper, threads per inch with a pitch gauge, parallel against tapered, and the seat. What each one rules out, and where each one goes wrong.
A dash number is the tube outside diameter in sixteenths of an inch, not the thread size and not the bore. Why a -08 JIC has a 3/4 in thread, why a -08 ORFS has a bigger one, and why a pipe trade size is a different system again.
7 min read
Nearly every persistent leak comes from one of five things: two different cone angles, a parallel thread with nothing at the face, a tapered thread in a parallel port, a missing or damaged O-ring, or a joint tightened past the point where tightening helps.
Working, proof and burst pressure, the 4 to 1 design factor, why the same size has two different ratings depending on whether the stud is straight or adjustable, and why five of the ten standards on this site carry no published rating at all.
European, Japanese and Korean equipment arrives with BSPP, BSPT, metric 24 degree, JIS 30 degree and Komatsu connections, several of which look like something North American and none of which are. What to expect by origin, and what to check first.
If you have a fitting in your hand and no idea what it is, read how to measure one and then feed the four readings into the fitting identifier. If you already know which two families you are choosing between, the comparison pages answer that directly.
If a joint is leaking after it has been pulled up, start here - the cause is usually an arrangement that cannot seal rather than a torque figure. And if you are reading a pressure number off a catalogue, this one explains what that number is a rating for.
Every guide is free and needs no account. Every figure quoted in one is published on the size page it came from, with the sources behind it. Pressure ratings are safety-relevant and are only published here where two independent sources agree under conditions they both state; confirm any rating against the manufacturer specification for the exact part before a system is charged.