Selecting a Pneumatic Cylinder Rod Clevis and Pin as One Joint

The selection rule: specify the clevis as an assembly interface, not a single catalogue item. Confirm the rod thread, fork gap, pin bore, mating eye width, pin length and groove, retention method, loading and available swing. A standard reference narrows the geometry; it does not prove the whole joint is suitable.

The Dongzhou clevises, clips and pins range includes several connection styles. This page deals with a narrower question: how do the parts at one pinned rod-end connection actually fit together?

ISO 8140 is a mounting-dimension standard, not a complete part approval

ISO 8140:2018, as published by the Dutch standards body NEN, specifies mounting dimensions needed for the interchangeability of pneumatic-cylinder rod-end clevises. The scope includes its 1,000 kPa cylinder series, with cylinders made to ISO 6432 and ISO 15552 among the intended uses, while allowing other applications.

That scope matters. It does not tell a buyer that any two M12 clevises have the same thread pitch or that a particular pin-and-clip combination is approved. It also does not replace the current drawing and strength check for Dongzhou's offered material and exact size. NEN-ISO 15552:2018 covers the basic, mounting and accessory dimensions of a defined series of detachable-mounting pneumatic cylinders, again addressing interchangeability rather than every application load.

Our working position for a drawing review is to use the standard as a starting envelope. The purchase drawing must still close the interfaces that a standard title cannot: thread pitch and hand, eye thickness, the pin's working length, groove and retainer, finish and the permitted operating load.

The first trap: the thread fits on paper, but the pitch differs

The Dongzhou FK product table contains both regular and fine-pitch variants under the same nominal fork size. The examples below come directly from that table; they are not a universal ISO thread schedule.

The product page also defines LH as left-hand and FGLH as fine-pitch left-hand. Include the full suffix on the purchase order; do not assume the rod thread is right-hand.

A second fork choice changes how it attaches to the rod. Dongzhou lists FT male-thread clevises separately from the FK internal-thread range. Specify the rod-end thread gender before comparing lengths or ordering a pin.

Then check the fork, eye and pin as a stack

Pin diameter alone cannot identify a suitable pin. The PF clevis pin page has fields for nominal pin diameter, length, reduced groove diameter and groove-related dimensions. That is the right level of detail for procurement. A pin can pass through both holes yet leave no usable groove outside the fork, or it can project too far into adjacent motion.

Read the pin from the outside inward

Start at the retainer groove and outer fork face, then check the first fork leg, eye, second fork leg and the opposite pin end. This direction of review makes a short pin or misplaced groove obvious before production.

For example, the PF6 row identifies a 6 mm nominal pin and a 17.0 mm listed length. That is still insufficient to approve a joint: the fork gap, eye width and groove position must be checked on the same drawing.

During a drawing review, we would inspect four interfaces: pin to fork hole, pin to eye bore, eye width to fork gap, and the retainer's location beyond the fork. The joint must rotate through its required plane without the eye rubbing a fork leg or a nearby bracket. We do not publish a universal side-clearance or pin-fit number because the correct value depends on the approved drawing, load and bearing arrangement.

The catalogue itself shows why retention needs a controlled drawing

Dongzhou offers several retention routes. The PM-K page describes hand-removable metric safety clips for FK joints and calls them an alternative to PM-S. The PM-S page says its clips are for FK and FT joints with PM clevis pins. The PM-E page says its DIN 471 circlip is used with PF clevis pins. The PM-F page describes a DIN 6799 retaining washer for a PM bolt.

The distinction matters because a retainer is part of the axial load path. A clip can appear to fit a shaft while the groove diameter, width or distance from the fork is wrong. If the chosen route is a folding spring pin rather than a separate PF pin and clip, Dongzhou's CL series page lists explicit FK mates such as CL 6X12 for FK 6X12. That is a different assembly choice and should be called out as such.

What a drawing-ready clevis order looks like

Dongzhou's site shows assembled alternatives, including an FK/FT clevis, bolt and PM-K clip joint with example code FK6×12-ASSY/03, and a clevis with folding spring pin example FK6×12-ASSY/01. These examples confirm that the retained joint can be ordered as an assembly. They do not prove that a loose clip from another route is interchangeable.

One code is useful; one drawing is better

The assembly code reduces ambiguity only when the revision-controlled drawing states exactly which fork, pin or bolt, clip and finish are supplied. For a replacement or custom version, request the same detail instead of relying on a photo.

1. Identify the rod. Give the cylinder model if available, but also write the full male or female thread designation, pitch, hand and usable engagement.
2. Define the fork and eye. State FK or FT family, fork gap, hole size, mating eye bore and width, and the plane and range of rotation.
3. Define the pin. Specify diameter, working length, head or end form, groove position and material. Include push and pull forces and any end-stop shock in the application note.
4. Close the retention choice. Use the approved clip or circlip designation from the current controlled drawing, especially where the public pages disagree.
5. Set inspection points. Identify dimensions that must be checked on the delivered assembly, plus free rotation and positive axial retention after installation.

Our practical recommendation is to send the assembly section with the RFQ, even when asking for a standard part. Dongzhou states that it can make non-standard parts from drawings or samples, but a sample cannot reveal intended tolerances, thread class, material condition or allowable load by itself. Those details belong on the approved drawing.