What does "bore" mean here?
In this article, "pin bore" means the diameter of the hole in the rod end that the pin passes through. It is not the cylinder bore.
The cylinder bore is the inside diameter of the barrel, the tube the piston moves in. The pin bore is the hole the pin goes through. In a spherical rod end, it is the hole in the inner ring. Some guides to whole cylinders use "bore" for both, so when you talk to a supplier, say which one you mean.
What should you do before measuring?
Make the cylinder safe.
Fully retract the rod, support the load mechanically, and only then measure. Release the pressure and lock out the power unit before disconnecting any hose. Never measure the extended rod length while the cylinder is holding a load. If you are not sure how to make the machine safe, ask a trained technician to do it.
What do you measure?
| What | How | Common mistake |
|---|---|---|
| Type | Look for a ball inside a ring, a grease nipple (the fitting for adding grease), a threaded or welded neck, or a clamp slot | Treating a plain eye and a spherical rod end as the same part |
| Pin hole diameter | Use a caliper (a sliding measuring tool) or an inside micrometer. Measure in two directions at right angles, and at two depths. Measure the pin as well | Taking one reading, or ordering to the biggest reading on a worn hole |
| Widths | Record the bearing or inner-ring width, the body width, the opening of the fork or bracket it sits in, and the lug thickness (the thickness of the ear the pin passes through) | Recording only one "width" |
| Thread | Outside diameter. Pitch (the distance between threads) with a pitch gauge, which is a set of thread-shaped blades. Thread length. Inside or outside. Right- or left-hand | Guessing the pitch by eye, or telling inch from metric by diameter alone |
| Lengths and diameters | From the centre of the pin hole to the end of the thread or the shoulder. Overall length. Body outside diameter. Shoulder or neck diameter | Measuring from the wrong reference point |
| Grease and retention | Whether a grease nipple is fitted, and where. How the bearing is held: staked (the metal is bent over it), or with a retaining ring (see K02-Q1-10) | Leaving it off the drawing |
A measuring checklist for pin-mounted cylinders covers pin diameter, pin hole diameter, lug thickness, fork opening, mount width, centre-to-centre length and bearing width. For rod-end threads it adds outside diameter, threads per inch or metric pitch, thread length, inside or outside, and shoulder diameter.
A worn pin hole can become oval. Using only its largest diameter can lead to the wrong replacement. If you have an unworn pin or bushing, measure that too.
Why is the hole size alone not enough?
Because the pin and the thread are chosen separately.
SYZ builds to customer drawings. In the configurations listed in its HCR range, the rod thread depends on the series as well as on the hole size:
| Pin hole | HCR12CE | HCR12S | HCR20N and HCR20U | HCR25D |
|---|---|---|---|---|
| 20 mm | M16×1.5 | M14×1.5 | M16×1.5 | not listed |
| 25 mm | M20×1.5 | M16×1.5 | M16×1.5 | M18×2 |
The HCR10C and HCR15N pages do not list a thread at all. So with those series, a 25 mm pin hole tells you little about the thread. Measure and report both.
Which thread system is it?
Check the cylinder standard first, then the thread.
Many rod-end thread styles exist, but the most common are the NFPA styles: standard male, standard female and intermediate male. Metric fine threads, such as M20×1.5 and M27×2, are standard on ISO 6020 and 6022 cylinders, and UNF inch threads are common on NFPA-style cylinders (this is one cylinder maker's guide, Isohydraulic, so check it against the cylinder drawing or the standard). BSP threads are port threads, for hoses and fittings. They are not rod-end threads, and should not be confused with them.
A pitch gauge matters because an inch thread such as 1-14 UNS (a common size on NFPA rod ends) is not interchangeable with a metric thread, even when the diameters look close. Telling inch from metric, measuring pitch and finding the hand (left or right) are general thread skills. syzmachine.com covers them, and how to tell and specify the hand is covered in K01-Q1-01.
How should a worn part be recorded?
As it is.
Write something like "pin about 25 mm, eye hole visibly oval", and give both readings. Ordering from the largest worn reading can get the wrong part. Check an inside thread with a thread gauge, or by trying a mating outside thread. A caliper alone is not enough.
What should you send when asking for a replacement?
Everything above, plus a photo, the load and how the joint moves. A replacement order typically needs the old part number, or a clear photo showing the hole size, thread, overall length, load and articulation.
FAQ
Is the pin bore the same as the cylinder bore?
Can I identify a thread by its diameter?
Which reading do I use if the hole is worn?
Related reading
- Q1-02 Types of rod ends and rod eyes
- Q1-12 Thread engagement and locking
- Q1-14 Pin selection
- K02-Q1-10 Pressing the bearing into the eye
- syzmachine.com: How to Measure Thread Size: Diameter, Pitch, and Reading the Callout