The accessory at the end of a cylinder rod decides how force enters the machine and which movement the joint permits. Choose it as part of the load path, not as hardware added after the cylinder is sized.
Choose a pneumatic cylinder accessory by the movement it must allow and the force path it must carry. A rod clevis creates a pinned joint that swivels mainly in one plane. A knuckle eye provides the mating eye. A pin and retainer complete the pivot. A rotating-shaft clevis or self-aligning coupling accommodates a specific additional movement. Then verify rod thread, engagement, pin geometry, material, finish, environment and current load data for the complete assembly.
A cylinder can be correctly sized and still bind because its connection geometry is wrong. The rod may be asked to carry side load, the pin may not sit across both fork legs, or a retaining clip may be fitted to the wrong groove. These are interface problems, not pneumatic problems.
From a factory perspective, the best accessory enquiry shows the cylinder, guided load and connection in one section view. That drawing reveals whether the joint needs one-plane rotation, multi-direction articulation or compensation for a small assembly offset. A product name alone does not.
1. What the main cylinder accessories do
Rod clevis or fork end
A threaded fork mounts to the piston rod and accepts a mating eye plus pin. It permits pivoting mainly in one plane. Festo's official guide describes its SG clevis this way and links the form to ISO 8140 or DIN 71752.
Knuckle eye
An eye that fits between clevis legs and rotates on the pin. Eye width and bore must match the clevis gap and pin; the thread must match the cylinder rod or mating link.
Clevis pin and retainer
The pin transfers joint load across the fork and eye. A circlip, safety clip, retaining washer or other specified feature prevents axial escape. Pin and retainer form one designed interface.
Floating or self-aligning coupling
A coupling between piston rod and moved part that accommodates limited radial and angular misalignment defined by its maker. It helps with small offsets but does not correct poor machine guidance.
Rotating-shaft clevis
A clevis with a rotatable shaft adds motion at the threaded side. Dongzhou's FKR page states that it can compensate for radial movement or misalignment and that moving contact parts should be lubricated.
Complete clevis assembly
A fork, pin or bolt, washer and retaining element supplied as a matched set. The drawing must still control thread, gap, pin dimensions and retention details.
The official Festo piston-rod attachments guide distinguishes one-plane clevis rotation from the radial and angular compensation of a self-aligning rod coupler. Parker's official metric cylinder accessory locator groups rod clevises, eye brackets, pivot pins and plain rod eyes as related interfaces.
2. Select the joint by permitted motion
| Connection need | Likely route | Movement allowed | What it does not solve |
|---|---|---|---|
| Simple pivot in one known plane | Rod clevis, mating eye, pin and retainer | Rotation around the pin axis | Out-of-plane offset, poor guidance or pin bending |
| Pivot plus rotation at threaded side | Rotating-shaft clevis | Pin rotation plus model-specific shaft rotation | Unlimited radial load or unspecified misalignment |
| Small offset between rod and guided load | Floating or self-aligning coupling | Model-specific radial and angular compensation | Loose guides, bent frames or badly positioned cylinder |
| Direct eye between fork legs | Knuckle eye, clevis and pin | Pin-axis rotation | Thread mismatch, side thrust or undersized pin |
3. Follow the force from rod to machine
Every step can govern. Check push and pull force at actual pressure, dynamic peaks, shock at end stops, thread engagement, clevis section, pin shear and bending, bearing pressure in the eye, fork spreading and attached-link strength. Check extension and retraction separately.
Do not copy a load rating from a visually similar part. Ratings depend on material, heat treatment, dimensions, thread, pin support and the maker's definition. Dongzhou's current product tables contain load figures whose visible unit is not identified, so this guide intentionally does not reproduce them. Request unit-labelled data and a controlled drawing for final selection.
4. Threads, pins and retainers cause most ordering errors
Thread callout
State thread system, nominal diameter, pitch or threads per inch, internal or external form, right-hand or left-hand direction, usable engagement and any jam nut or shoulder. Dongzhou's FK clevis page lists suffix routes for fine pitch, left-hand and fine-pitch left-hand threads. Those options work only when the mating rod is equally clear.
Pin stack
Control pin diameter, usable length, fork inside gap, eye width, side clearance, washer stack, groove position and retained end. Too much side clearance permits impact and skew. Too little can clamp the eye when the retainer is installed.
Retaining feature
A clip is not interchangeable because it looks close. Dongzhou's category lists PM-S retainers, PM-E circlips and PM-F retaining washers for different pin or bolt arrangements. Match the standard and groove geometry to the exact pin. Parker's official accessory locator likewise separates rod clevis, eye and pivot-pin drawings while keeping them in one connection family.
5. Choose material and finish from the environment
Dongzhou's live pages list several routes across the range: Q235A carbon steel, medium-carbon steel 45, stainless options and 6061 aluminum, with product-specific finishes such as oil, zinc, nickel, passivation or anodizing. Availability varies, so these are page-listed options, not a promise that every material is available in every size.
- Indoor industrial use: define corrosion exposure, coating, lubrication and likely handling damage.
- Washdown or outdoor use: identify water, cleaning agents, salt and other chemicals. “Stainless” still needs an exact grade.
- Moving contacts: define lubrication for pins and rotating interfaces. A coating does not replace a wear plan.
- Mixed materials: consider galvanic compatibility, thermal expansion and the strength of the complete joint.
6. Dongzhou accessory routes
| Family | Page-listed role | Confirm before ordering |
|---|---|---|
| FK clevis | Metric fork end; page references DIN 71752, DIN ISO 8140 and CETOP | Thread suffix, gap, pin bore, material and finish |
| FKR rotating clevis | Rotatable shaft for specified radial movement or misalignment | Rotation, lubrication, thread and envelope |
| FE knuckle eye | Threaded eye for gas springs and pneumatic cylinders | Thread, eye bore and width, clevis and pin |
| FI self-aligning coupling | Floating-joint route for pneumatic cylinders | Exact compensation, thread, load and envelope |
| PF clevis pin | Metric pin for FK and FT joints; page states design for a DIN 6799 safety clip | Pin diameter, length, groove, retainer and material |
The standard references above describe the current product pages. They are not presented as independent certification. Put required standards, dimensions and inspection characteristics on the purchase drawing.
7. What our factory needs for a useful quotation
Dongzhou was established in 2006 and describes its work as R&D, manufacturing and trading of transmission and connection parts, including non-standard development from supplied drawings or samples. For a pneumatic accessory, a clear RFQ moves the discussion beyond “same as photo.”
- Assembly contextCylinder or rod thread, guided load, motion plane and a connection section view
- Forces and cyclePush and pull loads, pressure, speed, frequency, shock and required life
- InterfacesFull thread callout, fork gap, eye width, pin diameter and retention
- MisalignmentMeasured radial, angular or rotational need, not only “floating”
- Material and finishGrade, coating or passivation, corrosion environment and restrictions
- Quality requirementsQuantity, revision, critical dimensions, reports and sample approval
A physical sample helps reverse review, but it does not reveal material grade, heat treatment, tolerance intent or load history. We prefer to convert the approved result into a controlled drawing before production.
Need a cylinder connection that fits the whole assembly?
Send the rod thread, accessory drawing, mating-eye geometry and actual motion requirement. Dongzhou can compare them with current FK, FKR, FE, FI and pin ranges, or review a non-standard part from your drawing or sample.
About Dongzhou
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Frequently asked questions
What accessories connect a pneumatic cylinder rod to a machine?
Common rod-end accessories include a threaded clevis or fork, knuckle eye, clevis pin or bolt, retaining clip or circlip, rotating-shaft clevis and self-aligning or floating coupling. The correct set depends on the required motion, rod thread, pin geometry, load path and environment.
When should I use a rod clevis?
Use a rod clevis when the mechanism needs a pinned joint that swivels mainly in one plane. The clevis must match the cylinder rod thread and the mating eye, pin and retainer. It does not remove the need to align the cylinder and guided load.
What does a floating joint do on a pneumatic cylinder?
A floating or self-aligning joint links the piston rod to the moved machine part while accommodating the limited radial and angular misalignment specified for that exact model. It can reduce binding from small assembly offsets, but it is not permission to impose uncontrolled side load on the cylinder rod.
Can a clevis pin and retaining clip be mixed from different systems?
Do not mix them by appearance alone. Verify pin diameter and length, groove diameter and position, clip standard, fork gap, eye width, washer stack, material and corrosion protection. A clip that installs may still have the wrong groove geometry or axial retention capacity.
What thread details are needed for a cylinder accessory?
Specify thread system, nominal diameter, pitch or threads per inch, internal or external form, right-hand or left-hand direction, tolerance class when controlled, usable engagement length and any jam nut or shoulder. A nominal diameter alone cannot identify the connection.
What should I send for a custom pneumatic cylinder accessory quote?
Send the assembly and part drawings, cylinder make or rod thread, push and pull loads, motion plane, expected misalignment, pin and retention details, material and finish, environment, quantity and inspection requirements. A physical sample can help, but the final order should use an agreed controlled drawing.
