Stem vs Flange Casters: How to Choose the Right Mount

Posted by Kyle Kim on Aug 16th 2026

Stem vs Flange Casters: How to Choose the Right Mount

You have a caster that has failed and you need to replace it. The wheel tells you nothing useful. What matters is how the caster attaches to the equipment, because that attachment determines whether a replacement fits, carries the load correctly, and stays put.

Before you can order, you need to identify three things:

The attachment style on the existing equipment: a receiving tube or threaded socket, or a bolted mounting face
The relevant dimensions of that interface: thread size, bore diameter, or bolt-hole pattern
Whether the replacement must match exactly or whether a different mount is the better specification

This article covers the two mounting types Carrymaster® casters use: stem and flange. We explain what each one is, when each is the right choice, and how to identify what your equipment already has before you order. We also define socket and expanding-adapter mounts briefly, since you may encounter them, and link to a separate article on plate-mounted casters.

The Two Mounting Types Carrymaster Casters Use

Carrymaster casters are available in two mounting configurations. Every product in the leveling, non-leveling, and medical plastic ranges uses one of these two.

Mount	How it attaches	What the equipment needs
Stem	A shaft that fits into a receiving tube, socket, or threaded hole in the equipment	A compatible receiving interface: correct bore, thread, or retention groove
Flange	A flat mounting face fastened to the equipment with bolts through a fixed bolt pattern	A flat mounting surface with a matching bolt layout

A stem transfers the caster's load through a single shaft. A flange distributes it across a bolted face and multiple fasteners.

Those two sentences describe a load-path difference, not just a fitting difference. That distinction is what this article is built around.

Scope note: Zambus supplies stem and flange mounting only. Plate-mounted casters are covered in a separate article on this site. Socket and expanding-adapter mounts are defined later on this page for reference; they are not products Zambus supplies.

How to Identify What You Already Have, and What Size Stem You Need

This is the section most replacement buyers need before anything else. A caster that looks right from the outside can still be incompatible if the stem diameter, thread pitch, or bore retention style does not match the equipment's receiving interface.

What to record before you order

Work through this list before contacting us or placing an order. Each item narrows the field to the products that will actually fit.

Attachment style. Is there a hole or tube in the equipment that the old caster shaft slid into, or is the caster bolted to a flat face? This tells you stem versus flange immediately.
Receiving feature detail. For a stem mount: is the hole threaded, smooth-bored, or does it use a retention clip or groove? For a flange mount: how many bolt holes, and what is the spacing?
Relevant dimensions. For a stem: the bore diameter or thread size of the receiving hole. For a flange: the bolt-hole pattern dimensions. Measure the equipment interface, not the old caster, because a worn or damaged caster may have distorted dimensions.
Stem retention style. Threaded stems engage a threaded socket. Grip-ring stems lock into a smooth bore with a retention ring. Round stems fit a smooth bore without a thread. These are not interchangeable.
Overall height requirement. The replacement must match the equipment's working height. Record the existing caster's installed height before removing it.

When the stem size does not match

If your equipment uses an M12 stem interface and the caster you need is specified with a different stem, a size mismatch does not always mean the caster is wrong for the application. The Carrymaster M12/M16 Adaptor Stem is a purpose-built component that addresses confirmed M12 or M16 interface mismatches. It is not a universal solution and it does not substitute for verifying the full fitment before ordering.

When to ask rather than measure

Stem fitment is specific. Thread pitch, bore tolerance, and retention geometry all matter, and a measurement taken from a worn interface may not be accurate enough to confirm compatibility. If any dimension is unclear or the existing caster is no longer intact, contact us with the equipment make, model, and the original caster's part number if it is readable. We will confirm the correct product before you order.

Stem Mounting, and When It Is the Right Choice

A stem mount carries the caster's full load through a single shaft. That shaft fits into a receiving tube, threaded hole, or bored socket in the equipment frame. The receiving interface is part of the load path: its bore tolerance, thread engagement, or retention geometry directly affects how securely the caster is held and how the load transfers.

Stem mounting is the right choice when:

The equipment already has a compatible receiving interface and the replacement must match it
The equipment was designed around a specific stem type (threaded, grip-ring, or round) and changing the mount type is not practical
The application calls for a compact attachment point and the frame cannot accommodate a bolted flange face
You are replacing a failed stem caster on medical, laboratory, or light industrial equipment where the receiving socket is part of the equipment's structure

Stem mounting is not the right choice when:

The equipment's frame has no receiving tube or socket and adding one is not feasible
The load or application calls for attachment across a bolted face rather than through a single shaft
The existing stem interface is damaged, out of tolerance, or cannot be confirmed as compatible with the replacement stem

Stem types in the Carrymaster range

The Carrymaster non-leveling and medical plastic ranges use three stem configurations: swivel stem (SS), swivel round stem (SRS), and swivel grip-ring stem (SGR). The leveling range uses a plain stem (S). These are distinct products with different receiving-interface requirements. Confirming which type the equipment uses is part of the fitment check in Section 3, and is not interchangeable between types.

Flange Mounting, and When It Is the Right Choice

A flange mount attaches the caster to the equipment through a flat face bolted to a matching surface. The load is distributed across that face and across multiple fasteners rather than concentrated through a single shaft. The equipment needs a flat mounting surface and a bolt layout that matches the caster's flange pattern.

Flange mounting is the right choice when:

The equipment is designed with a flat mounting face and a bolt layout that matches a flange caster
The application involves higher loads or vibration where distributing attachment across multiple fasteners is preferable to a single shaft
The installation requires a caster that can be removed and reinstalled without disturbing the receiving interface
You are specifying casters for new equipment and can design the mounting face to match the flange pattern

Flange mounting is not the right choice when:

The equipment has a stem-receiving interface and there is no flat face available for bolting
The frame geometry or access constraints make bolted installation impractical
The existing installation is built around a stem type and changing the mount interface is not part of the scope

Flange types in the Carrymaster range

The non-leveling range carries rigid flange (RF) and swivel flange (SF) configurations, including brake variants. The leveling range uses a plain flange (F). The medical plastic range uses swivel flange (SF) and swivel flange brake (SFB). If you are specifying for a non-leveling application or replacing a caster in a medical plastic range, confirm the flange configuration and bolt pattern against the equipment interface before ordering.

The Load Path Is the Real Decision

Mounting compatibility is a threshold: the caster either fits the interface or it does not. But the more useful question is whether the load path the mount creates is appropriate for the application.

A stem concentrates the load through one shaft and into one receiving point. The strength of that connection depends on the fit between the shaft and the receiving interface. A flange distributes the load across a bolted face, with multiple fasteners sharing the attachment load across a larger bearing area.

What the Carrymaster AC range shows

The AC leveling series offers both stem and flange versions across the lower and middle of the range. The AC-300S and AC-300F, for example, are both rated at 551 lbs/ea. Within the same model, the mounting type does not change the load rating.

At the top of the AC range, the AC-1800F is offered in flange only. It carries 3,307 lbs/ea. No AC-1800S exists in the current catalog.

That is an availability fact, not a rule about which mount carries more. The AC-300 pair demonstrates that stem and flange can share an identical rating within the same model.

What the catalog does show as capacity rises is a change in the flange interface itself. The AC-1800F has a 3.94 in outer flange face and 0.51 in bolt holes. The AC-300F has a 2.87 in outer face and 0.26 in bolt holes. More bearing area and larger fasteners as the load increases. The interface scales with the load path it has to carry.

Key point: choose the mount the equipment interface requires. Then confirm the product's rated capacity covers the application load. These are two separate checks.

Mounting on a Leveling Caster Specifically

A leveling caster adds an adjustment mechanism to the mount decision. The mounting type and the leveling function are specified together, not sequentially.

Before specifying a leveling caster, confirm all three of the following:

The mount type the equipment interface requires. Stem or flange, confirmed against the equipment's receiving feature or mounting face. The AC leveling range carries both, so the interface determines the product suffix, not the other way around.
The load the caster must carry. Leveling casters are rated per unit. Confirm the per-caster load requirement against the product's rated capacity. For guidance on calculating the load per caster from total equipment weight, see our article on caster wheel load capacity.
The product-specific adjustment arrangement. Each leveling caster model has its own adjustment mechanism. Review the PDP for the specific product you are specifying. The AC-300S and AC-300F share the same height specification (3.23 + 0.39 in) and the same ABS handle. Within a model, the mount does not change the leveling function.

For the full range of stem and flange leveling casters, see the leveling casters range.

Other Mounting Types You May Encounter

Two other mounting types appear in the broader caster market. Zambus does not supply either.

Socket mount. The caster fits into a dedicated socket that is permanently attached to the equipment. The socket is a separate purchased component; the caster drops in and is retained by a pin or clip. Common on furniture and some light industrial equipment.
Expanding-adapter mount. A threaded or wedge mechanism expands inside a tube to grip the bore from the inside. Used where a stem cannot be threaded in and a retention ring is not suitable.

Neither type is available in the Carrymaster range. For industrial leveling and non-leveling applications, stem and flange are the specified mounting types.

If your existing equipment uses a plate-mounted caster and you are considering a replacement, see our article on plate-mounted casters for that decision.

Choosing for Your Equipment

Work through these four questions in order. Each one eliminates options before you reach the product level.

What does the equipment interface look like? A receiving tube, threaded hole, or retention socket means stem. A flat mounting face with a bolt pattern means flange. If neither is present, the equipment may need modification before a caster can be specified.
Is this a replacement or a new specification? For a replacement, the existing interface determines the mount type unless a change is being made deliberately. For a new specification, the mount type is a design decision and both are available.
Is the application leveling or non-leveling? Leveling casters are specified for equipment that needs to be leveled and stabilized in place. Non-leveling casters are for equipment that moves. The mount type is available in both categories.
Have you confirmed fitment at the product level? Category-level compatibility is not enough. Confirm the stem type, stem dimensions, or flange bolt pattern against the specific product PDP before ordering.

Where to go next

Replacement buyers looking for non-leveling stem or flange casters: browse the non-leveling casters range. For medical and laboratory equipment with plastic casters: browse the medical plastic casters range.

Leveling and machine specifiers selecting a stem or flange leveling caster: browse the leveling casters range.

To confirm fitment or request a quote, contact us directly. We will verify compatibility against your equipment details before an order is placed.

Frequently Asked Questions

1. What do the S, F, SS, SF, RF, SRS, SGR, and B suffixes mean in a Carrymaster model number?

Each suffix identifies the mounting configuration and swivel or rigid designation directly from the product title.

S = Stem (leveling range: "Stem Leveling Caster")
F = Flange (leveling range: "Flange Leveling Caster")
SS = Swivel Stem
SF = Swivel Flange
RF = Rigid Flange
SRS = Swivel Round Stem
SGR = Swivel Grip Ring Stem
B = Brake (appended to the base suffix, e.g. SFB = Swivel Flange Brake, SRSB = Swivel Round Stem Brake)

The suffix encodes the mount type and configuration. It does not encode load rating, wheel material, or frame material, which are product-specific and listed on each PDP.

2. What hardware is included with a stem caster versus a flange caster?

Stem and flange casters include different hardware because the attachment method differs.

The AC-0300S stem leveling caster ships with a stem and nut included. The nut secures the stem in the receiving interface. The AC-300F flange leveling caster ships with bolts and nuts included for installation to the mounting face.

Confirm the included hardware on the specific product PDP before ordering, since hardware specifications are product-level details.

3. What is a threaded stem caster?

A threaded stem caster uses a stem with an external thread that engages a matching threaded socket in the equipment. The thread provides positive engagement and prevents the caster from pulling out under load.

The AC-0300S is a threaded stem leveling caster. Its stem is M12 x 1.75 mm, confirmed from the live product page. This dimension applies to that specific model. Other stem casters in the range carry different stem specifications, and no stem dimension should be assumed to apply across the range.

4. What is the difference between a swivel stem caster and a swivel round stem caster?

Both are swivel stem configurations, but the stem geometry differs.

The ACMC-102SS is a swivel stem caster with an M12 x 25mm threaded stem. The ACMC-102SRS is a swivel round stem caster with a smooth round stem measuring Ø1.10 M8. Both models are rated at 264.55 lbs/ea.

A threaded stem engages a threaded socket. A round stem fits a smooth bore and relies on a separate retention method. The two are not interchangeable, and the equipment's receiving interface determines which type is correct.

5. Is the load rating per caster or for a set of four?

Load ratings in the Carrymaster range are per caster, not per set.

The ACSU-102SGR states 88.18 lbs/ea on its product page, and separately states 264.55 lbs with 4 casters. These are the same product: the per-set figure is the per-caster figure multiplied by four. When calculating whether a caster is rated for your application, use the per-caster figure and compare it to the load each individual caster will carry.

6. Why do two light-duty stem casters carry different load ratings?

Load rating is product-specific and depends on the full product specification, not just the mount type.

The ACMC-102SS is rated at 264.55 lbs/ea. The ACSU-102SGR is rated at 88.18 lbs/ea. Both are light-duty swivel stem casters, but they are different products with different frame, wheel, and stem specifications. The mount type alone does not determine the rating. Always verify the rated capacity on the specific product PDP for the model you are specifying.

7. Can I mix stem and flange casters on the same equipment?

Mixing mount types on the same piece of equipment is a design and fitment question, not a general rule.

If the equipment has different receiving interfaces at different mounting points, for example a stem socket at one corner and a flat mounting face at another, then different mount types may be the correct specification for each point. Each caster must be matched to its own mounting interface and load requirement independently.

If the equipment has uniform mounting interfaces, mixing mount types requires either modifying the equipment or using an adaptor, which introduces additional fitment variables. Confirm each mounting point independently before ordering a mixed set.

8. Can I replace a plate-mounted caster with a stem caster?

A direct swap is not possible without modifying the equipment, because the two mounts use different attachment interfaces.

A plate-mounted caster bolts through a top plate to a flat surface. A stem caster requires a receiving tube, threaded socket, or bored hole. If your equipment currently uses plate-mounted casters and you want to switch to stem, the equipment frame needs a receiving interface added at each mounting point. Whether that modification is practical depends on the frame material, geometry, and the load the new interface will carry.

For more on plate-mounted casters and how they are specified, see our article on plate-mounted casters.

9. Do medical plastic casters use different materials from the leveling range?

Yes. The two ranges are built for different environments and use different materials throughout.

The medical plastic range uses PA6 (polyamide) frames, TPR (thermoplastic rubber) or PP (polypropylene) wheels, and is designed for cleanroom, laboratory, and medical equipment environments where non-marking wheels and corrosion resistance matter.

The leveling range uses ALDC12 aluminum die-cast frames and PA6 wheels with NBR (nitrile butadiene rubber) components. It is built for industrial leveling applications where load capacity and stability are the primary requirements.

Both ranges are available in stem and flange configurations. The mount decision is separate from the material decision.

10. Are stem casters available in both leveling and non-leveling versions?

Yes. Stem mounting is available across both the leveling and non-leveling ranges.

The AC-300S is a stem leveling caster, rated at 551 lbs/ea, for applications where the equipment needs to be leveled and stabilized. The ACSU-102SS is a swivel stem non-leveling caster, for equipment that moves. Both use stem mounting but serve different functions and carry different specifications.

Confirm whether your application requires leveling or non-leveling function first, then select the stem configuration that matches the equipment interface.