A hydraulic cylinder with the correct bore, stroke and pressure rating will still fail early if its mounting arrangement is wrong. Side load from a mismatched mount wears the rod guide and seal bearings, and a mount that allows side load also lengthens the effective column length, reducing the rod’s buckling capacity without changing any of the published cylinder dimensions.
Mounting style is therefore not a detail to be settled after the cylinder is chosen. It determines how force enters the machine structure, whether the cylinder can pivot through its stroke, and whether the rod stays aligned from full retraction to full extension. This guide compares the standard mounting types, explains what each one does to the load path, and gives a decision path for choosing between them.
Fixed and pivoting mounts: the distinction that decides everything
Every cylinder mount falls into one of two families. Fixed mounts hold the cylinder in a fixed position and transmit force along the cylinder centreline. Pivoting mounts allow the cylinder to rotate as the mechanism moves through its stroke. Choosing between these two families is the first decision, and it is a question about how the load travels, not about what is physically convenient to bolt.
Side load is the mechanism that links mounting style to cylinder life. By the time side load shows up, the damage is already inside the cylinder. The most common signature is a rod seal that weeps within weeks of fitting, rod seal wear concentrated on one side only, or a gland area running warmer than the rest of the body. These are symptoms of a load path that is not along the axis, and they appear long before a bent rod would.
Mounting type comparison
| Mounting type | How the load enters the cylinder | Misalignment tolerance | Typical duty |
|---|---|---|---|
| Cap-end clevis (MP1) | Along the axis, pin jointed | Good in the pivot plane | Boom arms, tipping bodies, attachments |
| Detachable clevis (MP2) | Along the axis, bolt-on clevis | Good in the pivot plane | Serviceable pivot mounts |
| Trunnion (MT1 / MT2 / MT4) | Along the axis, integral pivot pin | Good in the pivot plane | Lifting mechanisms, compactors, presses |
| Rectangular flange (MF1 / MF2) | Direct along the axis | Low | Presses, test rigs, stationary machines |
| Head flange (ME5 / ME6) | Direct along the axis | Low | Where rod-end space is limited |
| Side lug (MS2) | Offset from the centreline | Low | Machine tools, light industrial |
| Cross tube mount | Pin through a welded tube | Good in the pivot plane | Mobile equipment, compact pivot mounting |
| Rod eye | Pin joint at the rod end | Good in the pivot plane | Almost all pivot-mounted machines |
| Spherical bearing rod eye | Pin joint with angular float | Multi-axis | Frames that deflect under load |
Design guidance for conventional piston-rod cylinders is to treat intentional radial rod load as zero unless the manufacturer publishes a side-load rating for that specific configuration. The rod is a push element, not a guide.
Fixed centreline mounts
Flange mounts
Flange mounts bolt the cylinder flat to a machined face on the machine and transfer force directly along the axis. They are the strongest option for straight-line pushing and pulling, and the only sensible choice when the load never changes direction relative to the machine.
Two details decide whether a flange mount works. First, the mounting face must be flat and fully supported — a distorted plate pulls the cylinder out of alignment and bolt preload becomes a bending load. Second, cap-end flanges suit thrust (push) and rod-end flanges suit tension (pull); the wrong end under the main force introduces bending into a flange that was not designed for it.
Side lug and foot mounts
Side lugs attach the cylinder along the barrel, which is compact and useful on machine tools. The limitation is structural: the force acts along the rod centreline while the mounting reaction acts beside or below it, so the mount and the machine frame must resist the resulting overturning moment. In light duty this is acceptable. On long cylinders the frame stiffness requirement becomes significant, and a rigid base with correct bolt preload is essential.
Pivoting mounts
Clevis mounts
A clevis mount uses a pin through the cap end, usually paired with an eye or clevis at the rod end. The pin allows rotation in a single plane, so the cylinder follows the arc of the mechanism it drives. This is the most common arrangement on excavator attachments, agricultural implements, tipping bodies and waste compactors.
Pin alignment is the whole job. A pin forced through misaligned brackets applies side load from the moment the cylinder starts to move — before any useful work is done. Specify hardened pins, suitable bushings and a lubrication route.
Trunnion mounts
Trunnion mounts use a cylindrical pivot integrated into the barrel near the cap, head or centre. They suit lifting mechanisms and compactors where the cylinder must rotate through a wide arc while carrying high load.
Trunnion position is a design decision rather than a catalogue detail. Moving the trunnion can solve an interference problem, but it also changes the effective column length and therefore the buckling behaviour. Every geometry choice collects its payment somewhere.
Cross tube mounts
A cross tube mount places a welded tube at one end of the cylinder so it can be pinned into the machine structure. It gives a compact pivot connection and is familiar in mobile equipment designs. Pin fit, weld quality and bracket geometry govern its long-term reliability.
Rod end connections
The rod end deserves the same attention as the base mount. Common options are a clevis, a threaded rod end, a spherical bearing and a plain eye. Spherical bearings tolerate angular misalignment in more than one plane and are the right choice where the machine frame flexes under load or where installation error is unavoidable. Plain eyes are compact but demand better alignment.
ISO 6020-2 and NFPA mounting codes
Standard mounting dimensions are what make a cylinder replaceable across manufacturers. Recording the code removes ambiguity from a replacement enquiry and is often the fastest way to identify a cylinder from an existing machine.
ISO 6020 mounting codes
| Code | Mounting type | Notes |
|---|---|---|
| ME5 | Head, rectangular flange | Rod-end mounting |
| ME6 | Cap, rectangular flange | Cap-end mounting |
| MP1 | Cap, fixed clevis | Fixed cap-end clevis |
| MP2 | Cap, detachable clevis | Bolt-on clevis for serviceability |
| MP3 | Cap, fixed plain eye | Plain eye mount |
| MP5 | Cap, fixed eye with spherical bearing | Angular misalignment tolerance |
| MS2 | Side lugs | Compact fixed mounting |
| MT1 | Head, integral trunnion | Pivot near the rod end |
| MT2 | Cap, integral trunnion | Pivot near the cap end |
| MT4 | Intermediate trunnion | Centre pivot, selectable position |
| MX1 | Both ends tie rods extended | Symmetrical tie-rod mount |
| MX2 | Cap tie rods extended | Single-end tie-rod mount |
| MX3 | Head tie rods extended | Single-end tie-rod mount |
NFPA mounting codes
| Code | Mounting type |
|---|---|
| MP1 | Fixed clevis |
| MP2 | Detachable clevis |
| MF1 | Front rectangular flange |
| MF2 | Rear rectangular flange |
| MF5 | Front flange, extra size |
| MF6 | Rear flange, extra size |
| ME5 | Front head flange |
| ME6 | Rear head flange |
| MS2 | Side lug |
| MS3 | Centre lug |
| MS7 | End lug |
| MT1 | Front trunnion |
| MT2 | Rear trunnion |
| MT4 | Intermediate trunnion |
ISO and NFPA use the same three-character logic, which is why MP1 means a cap-end clevis in both systems. The metric series and the imperial series are not dimensionally interchangeable, so a machine frame drilled for one envelope should not be assumed to accept the other.
How mounting style affects buckling capacity
Mounting style and stroke length cannot be specified independently. Two cylinders with identical bore, rod diameter and stroke can have very different resistance to buckling, because the mount determines the effective column length, the way the load is guided, and the bending moment transmitted into the rod.
The engineering chain runs in one direction:
Mounting style → load path → effective buckling length → rod diameter capability → seal and bearing life
A pivoted mounting gives a longer effective length and therefore a lower buckling capacity than a rigidly guided rod, even though the catalogue dimensions are identical. Where a long push stroke is involved, this is where bent rods come from. The remedies are a larger rod diameter, a stop tube, or an external guide to carry the radial component.
The practical rule for conventional piston-rod cylinders: do not design intentional radial rod load. If the load path cannot be brought onto the cylinder centreline, the answer is a different mounting arrangement or an external guide, not a rod diameter chosen to absorb it.
How to choose: a decision path
- Does the cylinder stay stationary while it works? If yes, use a fixed mount. If the load direction never changes relative to the machine, use a flange mount.
- Does the cylinder rotate through its stroke? If yes, use a pivoting mount. Choose a clevis for serviceability, a trunnion for high load in a wide arc, and a cross tube where installation space is tight.
- Can the load be brought onto the centreline? If not, do not compensate with a heavier rod. Change the mount or add an external guide.
- Does the machine frame flex or is installation tolerance poor? If yes, use a spherical bearing rod eye to take up angular error.
- How long is the stroke relative to the rod diameter? If the stroke exceeds roughly ten times the rod diameter, run a buckling check before committing to a rod size.
- Is the machine a replacement job? Record the mounting code from the old cylinder. Matching the code removes the most common cause of a cylinder that does not fit the frame.
Specifications needed to order a mounted cylinder
When requesting a mounted cylinder, supply the mounting type in standard terms or by code, together with the pin diameter and pin-to-pin distance, the closed length, and the rod end style. For flange mounts, give the flange dimensions and bolt circle. These are the details that determine whether the cylinder fits the frame and whether the load path is correct.
Frequently asked questions
What mounting type is best for long stroke cylinders?
There is no universally best type, but a pivoting mount gives a longer effective column length and therefore lower buckling capacity at the same rod diameter. For long push strokes, either increase the rod diameter, specify a stop tube, or add an external rod guide. A rigidly guided flange arrangement is more favourable for buckling but cannot follow a curved load path.
Can I change the mounting style on an existing cylinder?
Rarely in practice. The mounting is welded or bolted to the barrel and gland, and changing it alters the effective length, the load path and the weld integrity. If a different arrangement is needed, it is usually cheaper and safer to select a cylinder built for that mounting.
What is the difference between a clevis and a trunnion mount?
A clevis mount uses a pin through a cap-end bracket, typically with a removable pin and bushing. A trunnion mount uses a cylindrical pivot integrated into the barrel. Both allow rotation in one plane; the trunnion carries higher load through a shorter, stiffer connection, while the clevis is easier to assemble and service.
Do I need a spherical bearing rod eye?
Only where angular misalignment is unavoidable — for example on machines whose frames flex under load, or where installation tolerances are wide. It removes side load caused by angular error, but it does not make the rod a radial guide and it does not prevent side load from an off-axis load path.
How do I identify the mounting code on an existing cylinder?
Measure the mounting geometry and match it against the tables above: pin diameter and spacing for pivot mounts, flange outline and bolt circle for flanges. The code is often stamped on the barrel or cast into the mount, but on painted or unmarked cylinders the geometry is the reliable route.