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Hydraulic Cylinder Mounting Types: Complete NFPA Guide

Selecting the correct hydraulic cylinder mounting types is where specifications most commonly go wrong — and where failures are most preventable. The bore, stroke, and pressure rating get proper attention. The mounting style gets copied from the previous design or picked because it was in stock — and then the cylinder fails in six months from side loading it was never designed to handle.

The NFPA mounting code system standardizes every mounting style used in industrial and commercial hydraulic cylinders, from simple fixed-flange mounts for rigid presses to articulating clevis and trunnion mounts for pivoting linkages. This guide covers every NFPA mounting style with the mechanical logic behind each one, how to select the right mount for your load path, and what goes wrong when the wrong mount is specified.

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1. Why Mounting Style Matters

A hydraulic cylinder generates force along its centerline axis. Every mounting style is designed to manage that force — and whatever combination of off-axis loads the application introduces.

Three loading conditions determine your mount:

Pure axial loading: Force is applied exactly along the cylinder centerline, with no angular deviation throughout the stroke. Fixed mounts (flanges, foot mounts, side lugs) work here. The structure is rigid; the load path is straight.

Pivoting / articulating loads: The cylinder must swing through an arc as it extends and retracts — like an excavator boom or a dump truck hoist. If you rigidly mount a cylinder that needs to pivot, you build massive side loads into the rod and gland every time the system moves. Pivoting mounts (clevis, trunnion) allow the cylinder to follow the load path.

Off-axis / side loading: Any force that isn’t parallel to the cylinder centerline is a side load. Side loads attack the rod gland seal and the rod itself. They reduce seal life and, in severe cases, bend the rod or crack the gland. The mounting design either eliminates side loading through alignment (pivoting mounts) or resists it structurally (heavy-duty fixed mounts with guide systems).

The NFPA identifies mounting category by a two-letter code. The first letter indicates the mounting family (C = clevis, T = trunnion, F = flange, etc.); the second letter indicates the specific style within that family.

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2. Clevis Mounts (CB, CC, CD)

Clevis mounts allow the cylinder to pivot through one plane of rotation. The mount is a forked bracket (clevis) with a pin through the cylinder’s cap end (rear clevis) or an intermediate lug. The rod end typically has a matching clevis or rod eye to complete the articulating connection.

CB — Rear Clevis (Pivot Pin Through Cap End)

The most common pivot mount. The cylinder body is pinned at the cap end through a clevis bracket, allowing full rotation in the plane of the clevis pin. A rod eye or front clevis pin at the rod end completes the double-pivot arrangement.

Load path: Both ends pivot, so the cylinder follows the arc of the mechanism it drives. No side loading if alignment is correct and pin holes are properly bored and maintained.

Applications:

• Excavator and loader linkages
• Dump body hoists
• Agricultural implement cylinders (3-point hitch, grapple, blade tilt)
• Any mechanism where the cylinder must swing through an arc during its stroke
• Log splitter ram: clevis at cap end, rod end pushes the wedge directly

Sizing notes: Specify clevis pin diameter and pin-to-pin dimensions when ordering. Under-sized clevis pins in high-load applications cause galling and failure at the clevis bore. The standard recommendation is to use the full-rated clevis pin diameter for the cylinder bore, not a smaller pin because the hardware happens to fit.

What goes wrong: Clevis pins that aren’t maintained (greased per schedule) seize in the bore. A seized clevis pin turns the pivot mount into a fixed mount — all the angular displacement goes into the rod as side load. This is a common root cause of rod seal failure on mobile equipment.

CC — Intermediate Clevis (Pivot at Mid-Barrel Position)

A clevis bracket is mounted partway along the barrel, allowing the cylinder to pivot from an intermediate point. Less common than CB; used in designs where the pivot point geometry doesn’t align with the end cap.

CD — Cap Lug Clevis

A single lug welded or machined onto the cap end, accepted into a single clevis bracket. One pin, one pivot point at the cap end. Less common than CB in mobile applications; used in compact designs where a full clevis fork doesn’t fit.

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3. Trunnion Mounts (TB, TC, TD)

Trunnion mounts pivot the cylinder from a pair of coaxial pins (trunnions) projecting from either the cap end, head/rod end, or center of the barrel. The trunnion pins ride in bearing blocks mounted to the machine frame, allowing the entire cylinder to rotate around the trunnion axis.

TB — Cap End Trunnion

Trunnion pins project from the cap end plate. The cylinder pivots around this fixed point as it strokes.

Applications:

• Heavy industrial presses with pivoting upper ram
• Linkage systems where the pivot point must be at the rear of the cylinder
• Large construction equipment where the bulk of the cylinder mass must be supported at the cap end

Bearing requirements: Trunnion pins carry the full cylinder thrust load plus the weight of the cylinder in a cantilevered arrangement. Bearing blocks must be sized for the full cylinder weight plus applied load, not just the applied load. Inadequate bearing support causes trunnion pin bending and eventual bracket failure.

TC — Head End (Rod End) Trunnion

Trunnion pins project from the front (gland/head end) of the cylinder. The rod extends forward from the trunnion pivot point.

Applications:

• Applications where the load path puts the pivot point at the rod end of the cylinder
• Press designs with centrally-located actuators that must pivot in the frame
• Robotics and heavy automation systems with complex pivot geometry

TD — Intermediate (Center of Stroke) Trunnion

Trunnion pins project from the center of the barrel. This creates the most neutral load distribution across the trunnion bearings. When the cylinder extends and retracts, the weight moment arm to each bearing block changes minimally.

Applications:

• Large industrial cylinders where the cylinder weight itself creates significant bearing loads
• Heavy-duty forming and forging equipment
• Applications where balanced loading across the mounting frame is required

Design note: The trunnion center position must be specified at order time. It’s typically defined as the distance from the cap end or head end to the trunnion centerline. For applications with unequal extend/retract forces and stroke, trunnion position may be optimized to minimize bearing loads at the critical operating point.

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4. Flange Mounts (FB, FC, FE, FF)

Flange mounts rigidly attach the cylinder to the machine structure via a bolt pattern on a flange at the cap end or head end. They provide no angular articulation — the cylinder axis is fixed. They’re the correct choice when the load is purely axial and the machine structure handles alignment rigidly.

FB — Cap End (Rear) Square Flange

A four-bolt square flange on the cap end. The cylinder is bolted flat against the machine frame, rod extending forward. This is the most common flange mount style in industrial hydraulic machinery.

Applications:

• Industrial presses: ram extends down into the workpiece, cylinder body rigidly mounted above
• Material handling: vertical lifts where the cylinder body is fixed and the rod pushes a platform
• Machine tool clamps: cylinder body fixed to the machine structure; rod engages the workpiece

Bolt pattern: NFPA standardizes the bolt circle and hole size for each bore. Stud length and thread specification must match the mounting plate thickness.

FC — Cap End (Rear) Round Flange

Same concept as FB but with a circular bolt pattern. Used where a square bolt pattern would conflict with adjacent components, or in older machine designs that specify the round pattern.

FE — Head End (Front) Square Flange

Flange on the head/rod-end of the cylinder. The rod extends back (away from the work), and the cylinder body moves forward. Less intuitive than cap-end flange mounting but correct for applications where the rod must be anchored and the body travels.

FF — Head End (Front) Round Flange

Round flange at the head end. Same application logic as FE.

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5. Foot Mount (BB)

The foot mount (BB style) uses one or more mounting feet welded or bolted to the cylinder body. Bolts through the feet anchor the cylinder to a flat surface. The cylinder axis runs parallel to the mounting surface.

How it works: Mounting feet project downward (or sideways) from the barrel at approximately 1/3 and 2/3 of the barrel length. Bolts through the feet into a mounting plate or baseplate hold the cylinder in position.

Applications:

• Horizontal cylinder installations on machine frames
• Applications where flange mounting isn’t practical due to access or geometry
• Light-to-medium industrial machinery
• Horizontal material transfer equipment

Critical limitation: Foot mounts introduce bending moments into the barrel when the cylinder is under load. The applied load creates a bending moment at each foot, and if the feet aren’t evenly supported or the mounting surface isn’t flat, the barrel experiences combined bending and compressive loading. For high-force or long-stroke applications, foot mounts require careful structural analysis.

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6. Head Lug Mount (HB) and Cap Lug Mount (LB)

HB — Head Lug

A single lug on the head/rod end of the cylinder, with a pin hole perpendicular to the cylinder axis. Accepts a single pin in a single bracket. Simpler and more compact than a full clevis.

Applications: Compact machinery where space precludes a full clevis arrangement; low-to-medium force applications.

LB — Cap Lug

Equivalent to HB but located at the cap end of the cylinder.

Both lug mounts are intermediate options between fully fixed flange mounts and full pivot-capable clevis or trunnion mounts. They allow limited pivoting in one plane but have lower angular capacity than a full clevis pin arrangement.

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7. NFPA Mounting Code Reference Table

NFPA Code	Mount Style	Location	Pivot?	Typical Application
CB	Rear clevis	Cap end	Yes — 1 plane	Mobile linkages, dump hoists, ag equipment
CC	Intermediate clevis	Mid-barrel	Yes — 1 plane	Special geometry pivoting applications
CD	Cap lug clevis	Cap end	Yes — 1 plane	Compact pivot arrangements
TB	Cap end trunnion	Cap end	Yes — 1 plane	Heavy industrial, large press pivot
TC	Head end trunnion	Head/rod end	Yes — 1 plane	Complex pivot linkages
TD	Intermediate trunnion	Mid-barrel	Yes — 1 plane	Large cylinders, balanced bearing loads
FB	Rear square flange	Cap end	No — rigid	Industrial press, vertical lift, clamp
FC	Rear round flange	Cap end	No — rigid	Older designs, round bolt pattern clearance
FE	Front square flange	Head end	No — rigid	Rod-anchored, body-travels applications
FF	Front round flange	Head end	No — rigid	Round bolt pattern clearance
BB	Foot mount	Barrel sides	No — rigid	Horizontal cylinders, machine bases
HB	Head lug	Head end	Limited pivot	Compact pivot, moderate force
LB	Cap lug	Cap end	Limited pivot	Compact pivot, moderate force

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8. How to Select the Right Mounting Style

Follow this three-step process:

Step 1: Determine whether the cylinder needs to pivot.

Draw the mechanism at both extremes of the cylinder stroke. If the cylinder centerline angle changes between the retracted and extended positions, the cylinder must pivot. Use a clevis (CB) or trunnion (TB/TC/TD) mount. If the centerline remains fixed throughout the stroke, use a fixed mount (flange or foot).

Step 2: Identify where the pivot point must be located.

For a pivoting application: if the natural pivot point is at the cap end (rear), use CB clevis or TB trunnion. If the pivot must be at the rod end for geometric reasons, use TC trunnion or HB head lug. If a central pivot is needed for load balancing, use TD intermediate trunnion.

For a fixed application: if the cylinder body is stationary and the rod extends forward into the work, use FB or FC cap-end flange, or BB foot mount. If the rod must be anchored and the body is stationary, use FE or FF head-end flange.

Step 3: Verify the load path and check for side loads.

For clevis and trunnion mounts: confirm both the cap-end and rod-end pin connections are aligned. Misalignment at either end produces side loading on the rod. Use self-aligning rod eyes or alignment couplers when precise alignment can’t be guaranteed.

For fixed flange and foot mounts: confirm the cylinder axis is exactly aligned with the load direction. Any angular offset produces side loading on every stroke.

When side loading can’t be avoided: Specify an oversized rod diameter for the bore size. External guide rails eliminate cylinder side loading by taking that force out of the cylinder entirely — appropriate for high-cycle, long-stroke applications where minimal cylinder side load is critical.

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9. Application Examples by Mount Type

Log splitter: Clevis mount (CB) at the cap end. The cylinder pivots slightly as the wedge engages a log of varying diameter. Rod end pushes the wedge plate directly — no front pivot needed because the wedge plate constrains the movement. Double-check that the pivot pin is greased — log splitters are notoriously under-maintained.

Dump truck hoist: Clevis or trunnion at the sub-frame; rod end pushes the dump body hinge. The cylinder swings through a significant arc as the body raises from 0° to 45–55°. A CB clevis is most common on smaller dumps; trunnion mounts are used on larger trucks where the bearing load requires distributed support.

Industrial hydraulic press: FB cap-end flange. The press frame is rigid; the load path is purely axial (straight down through the workpiece). No angular movement, no pivot needed.

Agricultural grapple/bucket tilt: CB clevis at both ends. The grapple tilts through 90°+ of rotation; both ends of the cylinder must pivot freely. Clevis pins must handle the combined weight of the grapple plus load.

Machine tool clamp: FB flange or foot mount BB. The cylinder body is bolted rigidly to the machine structure. Rigid mount is correct — the clamp movement is linear, no angle change.

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10. Mounting Hardware Specifications

Clevis pin diameter: Match to the rated pin size for the cylinder bore and mounting lug. Undersized pins concentrate load at the pin contact area and cause rapid wear. Parker, Bosch Rexroth, and most manufacturers publish pin diameter recommendations in their cylinder catalogs — use those values, not whatever pin happens to be convenient.

Spherical rod eyes and alignment couplers: For clevis-mounted cylinders where precise alignment between the cylinder axis and the pin hole cannot be guaranteed, spherical rod eyes (also called ball joint rod ends) provide ±6–12° angular accommodation. These compensate for minor misalignment without transferring bending moments to the rod.

Misalignment couplers: Installed between the rod end and the external load attachment. Accommodate angular offset between the cylinder and the mechanism without side-loading the rod. Recommended for long-stroke cylinders and applications where thermal expansion or wear may shift alignment over the system’s life.

Mounting plate and frame design: The mounting structure must handle the full cylinder thrust force with appropriate safety factors. For flange-mounted cylinders, the bolt circle is in bending as the cylinder load applies an overturning moment to the flange. Use the manufacturer’s recommended mounting plate thickness — undersized mounting plates allow the cylinder to flex and can cause premature gland seal failure.

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Frequently Asked Questions

What is the most common hydraulic cylinder mounting style?

For industrial applications, the FB cap-end square flange is the most common — it’s the default for stationary industrial presses, machine tools, and material handling equipment. For mobile applications, the CB rear clevis is dominant because virtually every mobile application requires the cylinder to pivot as it extends and retracts.

What does CB mean on a hydraulic cylinder?

CB is the NFPA code for a rear clevis mount. The “C” indicates clevis family; the “B” indicates the specific style — rear (cap end) clevis. The cylinder body has a clevis bracket at the cap end, accepted into a mating clevis fork on the machine frame. A pin through both completes the pivoting connection.

What is the difference between a clevis and a trunnion mount?

Both allow the cylinder to pivot, but they locate the pivot point differently and distribute loads differently. A clevis mount (CB) pivots the cylinder from a pin through the cap end — the entire cylinder swings around that pin. A trunnion mount pivots the cylinder from projecting pins (trunnions) at the cap end, head end, or center of the barrel — the cylinder rotates around the trunnion axis, which is supported in bearing blocks on both sides. Trunnion mounts handle heavier loads because the pivot load is distributed across two bearing points rather than concentrated in a single clevis pin.

Can I use a flange-mounted cylinder in an application where the cylinder needs to pivot?

No. Flange mounts are rigid — they fix the cylinder axis to the machine structure. If the mechanism requires angular movement, the rigid mount will transfer all that angular displacement to the rod as bending stress. Rod gland seal life will be dramatically shortened, and the rod may eventually bend or crack the gland. If your application requires pivoting, specify a clevis or trunnion mount.

What happens if I choose the wrong mount for my application?

The most common failure mode from incorrect mount selection is premature rod seal failure from side loading. The next most common is rod bending or gland cracking in severe cases. Both typically appear within the first 20–30% of the expected cylinder service life. If a cylinder is failing at the rod seal consistently across multiple replacement cycles, mount selection and alignment are the first things to evaluate.

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For step-by-step hydraulic cylinder sizing that accounts for mounting geometry and side loading, see How to Size a Hydraulic Cylinder. For cylinder type selection before determining mounting style, see Types of Hydraulic Cylinders.

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NFPA mounting codes referenced in this article comply with NFPA/T3.6.7 R3. Consult the full NFPA standard and manufacturer engineering data for final design specifications.