Monitor Arm Parts and Accessories: Brackets, Screws & Plates

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Most monitor-arm hardware problems — a drooping arm, a VESA plate that will not sit flush, a clamp pressing a slow dent into the desktop — start with compatibility, so if you have not already confirmed that your display and arm match, begin with our VESA monitor arms compatibility guide before digging into parts. What follows assumes the pair is nominally matched and deals with the second layer: the screws, spacers, plates and mounting hardware that sit between the monitor and the desk.

Arms are sold as complete systems, and manufacturers rarely break the parts out into a shopping list. That makes replacement and diagnosis awkward. When a plate is missing from the box, when a screw will not reach its threads, or when a clamp needs reinforcement, there is no obvious catalogue to consult. The monitor-side interface is standardised; the desk-side and accessory hardware is not.

This is built as a diagnostic path rather than a parts list. Each section starts from a symptom you can see, gives you a measurement to take, and names the component that resolves it — using the exact figures manufacturers publish. Where two failures look identical from a metre away, the point is to tell them apart before you touch a screw.

It is written for anyone maintaining an existing arm: replacing lost hardware, adapting a monitor that does not match the mount, reinforcing a desk that flexes, or chasing a droop that keeps coming back.

Start by Separating Arm Sag From Head Tilt Droop

Downward movement of a monitor arm has at least two distinct causes, and they use different adjustment points. Treating one as the other is the most common reason a "sagging" arm never gets fixed.

If the whole arm assembly — pole section, forearm and monitor together — drifts downward while the screen keeps its angle, the lift mechanism has lost tension. On a gas-spring or counterbalance arm, that is the spring-tension screw, adjusted with the Allen key the arm shipped with. Increase it gradually and in small steps. On a mechanical Constant Force arm, the adjustment is the same idea with a different mechanism.

If instead the arm holds its height and only the monitor's nose tilts down or creeps, the fault is at the head. The tilt/head joint has its own friction fastener and it is tightened separately. Turning the gas-spring screw will not fix a loose tilt hinge — you will raise the whole arm and leave the droop exactly where it was. BenQ's guidance is to increase joint tension first and only then revisit load.

There is a stopping point on both adjustments. If the lift still sinks after the tension is correctly set, the cause is either that the mounted load exceeds the arm's rated range or that the mechanism is worn or defective. AVLT's position is explicit: persistent droop after correct adjustment justifies replacement or an RMA rather than another turn of the screw. Over-tightening a spring to compensate for an overloaded arm stresses the joint and does not restore a stable position.

An arm that climbs by itself points the other way. Counterbalance arms carry both a maximum and a minimum load; below that floor, the spring is too strong for the display and pushes it up. The fix is to reduce tension — and if the arm still rises, the monitor sits outside that arm's load window.

VESA Screws: Probably M4, and the Length Is What Matters

The monitor-side mounting standard is the VESA interface, and for computer monitors the two patterns that matter are 75×75 mm and 100×100 mm. Both take M4 screws in normal use. Dell specifies M4×10 for several of its monitor mounts, BenQ/ZOWIE specifies M4×10 for a 100 mm VESA interface, and Ergotron supplies M4×10 or M4×12 for 75×75 and 100×100 display attachment. The coarse metric pitches you will meet are M4 = 0.7 mm, M5 = 0.8 mm, M6 = 1.0 mm and M8 = 1.25 mm.

That M6 and M8 exist does not mean your monitor needs them. Those diameters show up in large-pattern adapters and in the arm's own clamp and grommet assemblies, not on a standard 75/100 monitor. BenQ's BSH-series hardware list makes the split plain: the display is fixed with four M4×12 screws plus D5 washers, while the clamp uses an M8×75 screw and the grommet uses an M8×150 screw.

The trap is length. A screw can have the correct diameter and pitch and still be wrong for your panel. LG documents a 100×100 monitor — the 27MU88-W — that uses M4×10 while capping thread penetration past the back-cover surface at 8 mm. The nominal screw is safe; a longer one of the same diameter is not. Recessed VESA cavities invert the problem: there the screw must be longer to reach, and rigid spacers or standoffs make up the added distance without letting the plate flex.

Anything you add between the monitor and the arm changes the length you need. Washers, spacers, an adapter plate and the arm's own VESA plate thickness all count toward how far the screw has to travel. That is why "it screws in" proves nothing — a screw that engages a thread is not automatically a screw that is safe to leave there.

If the screws are simply missing, a universal hardware kit covers the common cases. The WALI UVSP 68-piece set supplies M4, M5, M6 and M8 screws, washers and spacers — enough to replace lost VESA hardware and to test diameters before committing to a single length. What a kit cannot do is tell you which length is safe; that still comes from the monitor's own manual.

When the VESA Plate Will Not Seat: Pattern Mismatch vs. Recessed Cavity

Two different problems look the same from the front of the monitor, and they take different parts.

The first is a pattern mismatch: the hole spacing itself does not line up. If the monitor's holes are 100×100 and the arm's plate only offers 75×75, you need a conversion plate that bridges 75 to 100. If the monitor uses a larger pattern — 200×100 or 200×200 — the arm's 75/100 plate will not reach at all. The VIVO MOUNT-AD2X2 is a steel adapter that converts a smaller interface up to patterns as large as 200×200 mm, marketed for roughly 23–42 inch displays. Mount-It's MI-788 kit converts 75×75 or 100×100 to 200×100 or 200×200 mm in heavy-gauge steel, listing 66 lb of capacity that remains subject to the arm's own limit, and shipping M5×12 hardware for the mount side with M6×14, M8×20 and spacers for the display side.

The rule that catches people out: an adapter plate does not increase the arm's weight capacity. It converts geometry. The plate's own mass counts against the arm's limit, and a bigger pattern does not make a heavier monitor safe on an arm that was never rated for it. Recalculate the total mounted load — monitor plus adapter plus anything else attached — before you trust the arm.

The second problem is clearance. The screw-hole spacing matches, but the plate cannot sit flat because the VESA area is recessed into the monitor shell. A generic plate that matches the 75×75 spacing can still foul a circular or deeply recessed cavity. This is a physical clash, not a pattern problem, and switching to a differently branded 75×75 plate will not solve it. BenQ's answer for its own arms is M4×12 standoff spacers or a compatible adapter plate when its square VESA plate conflicts with a circular recessed back; the standoffs lift the plate clear of the cavity so it can sit flat.

If the monitor has no VESA holes at all, the geometry problem is bigger. A universal non-VESA adapter grips the chassis and outputs a VESA interface. HUANUO's HNMUA4 is alloy steel and is what HUANUO points owners to when a monitor lacks mounting holes. Treat the size guidance on these adapters as a starting point only: HUANUO's arm documentation says "most monitors" up to 32 inches while the product catalogue describes roughly 17–27 inches, a conflict that means you should check the actual bezel width and height rather than the diagonal. A grabber adapter also adds weight, depth and leverage, so it is not equivalent to a native metal VESA interface for load purposes.

Reinforcement Plates: Spreading Clamp Load, Not Fixing the Desk

A C-clamp concentrates the entire weight of the monitor and arm onto a small pad on the underside of the desktop. On thin boards, MDF and particleboard, that concentration shows up as a dent, a crease or slow deformation around the clamp. The symptom is visible from below: a depression where the clamp has been sitting, or an edge that flexes when the arm moves.

A reinforcement plate is the direct fix for that symptom. It does not reduce the load; it spreads it over a larger bearing surface. The VIVO STAND-AC01R is a 2.5 mm steel plate with a 7.9 × 6.1 inch main section and a 6 × 2 inch support plate, supplied with a padding strip. VIVO describes it as compatible with "most" C-clamps rather than every clamp, and positions it for thin desks, glass tops and fragile surfaces. HUANUO's HNDA1 is the plate HUANUO names in its own arm manual for thin particleboard and glass, and it can be installed above or below the desktop. The WALI CGRP-B covers both grommet and C-clamp installations, which makes it the option to look at when the clamp path is blocked but the desk still needs reinforcement.

Two figures matter before you buy. First, a plate adds thickness between the clamp jaws, so the clamp may no longer open enough. BenQ publishes the effect on its own arm: the supported desktop range narrows from 17–50 mm without reinforcement plates to 12–45 mm with both fitted. A thick plate plus its padding can push a desk that was inside the clamp's range out of it. Second, a plate does not make a structurally unsuitable top suitable. Reports from lightweight, hollow-core desks describe some indentation even with a plate installed, because the plate spreads load across a surface that is itself giving way. If the top is genuinely hollow or the edge visibly flexes under the arm, a plate is one input, not a guarantee.

The most common fit failure is not the desk at all. A plate frequently collides with a desk frame, a shelf, a leg plate or a crossbar, forcing either a different clamp position or a different mounting method. If the plate cannot sit flat against a clear section of the underside, the reinforcement has nowhere to bear.

Grommet Mounting Hardware: There Is No Universal Hole Size

Grommet mounting threads a bolt through a hole in the desktop instead of gripping the edge. It is the standard escape route when a C-clamp cannot seat — a rear lip, a bevel, a drawer or a structural apron in the way — or when the clamp geometry simply will not clear the desk. The trade-off is a fixed anchor point rather than a repositionable clamp.

The single most useful thing to know is that there is no universal grommet size, and the numbers vary more than most people expect. HUANUO's HNCM12 specifies an 11–22 mm hole and a mounting surface 20–80 mm thick. BenQ's BSH-series accepts a 12–60 mm opening. Ergotron's 98-035 grommet kit fits holes from 8–50 mm across and worktops up to 76 mm thick, and includes the grommet plate, bolt, wing nut, T-wrench and cable ties. Those ranges only partially overlap, so an existing desk hole that suits one arm may be entirely wrong for another.

Grommet kits are also model-specific at the arm end. Ergotron's 98-035 is compatible with specified LX Dual and Tall Pole models, not every Ergotron arm, and some LX models ship with their own grommet hardware while others need the kit separately. Duronic's DM-GR-01 converts an appropriate Duronic C-clamp mount to a bolt-through attachment, but only for the DM15, DM25, DM35 and DM45 ranges. A grommet adapter is not a universal part that fits any pole.

Existing holes raise their own questions. If the hole is too small for the bolt, you can only enlarge it if the desk material and its manufacturer allow it. If the hole is too large, the bearing plate or washer under the desk may not have enough surface to hold — a larger plate or reinforcement washer is the remedy. If the desk is too thick for the supplied bolt, the answer is the arm maker's extended hardware, never a workaround that leaves threads under-engaged.

Quick-Release Brackets and Extensions Change What Your Arm Can Carry

Some parts solve a usability problem but quietly move the load math against you.

A quick-release bracket lets you lift the monitor off the arm without unscrewing four VESA screws each time. Ergotron's 60-589-060 fits 75×75 and 100×100 mm, ships with bracket, screws, standoffs and manual, and is rated to 35 lb / 15.9 kg for the bracket itself. It also adds roughly 1.2 lb / 0.54 kg and about 0.5 in / 1.2 cm of depth, so Ergotron states plainly that it slightly reduces the usable capacity of the attached arm, and does not recommend it for monitors deeper than about 3 inches without checking with the manufacturer. A quick-release plate is not a weightless convenience.

An extension arm adds reach. Ergotron's 45-289-216 LX Extension adds 9 in / 23 cm in aluminium, and only one extension is permitted per LX configuration — it is not intended for LX dual-monitor arms. The trade-off for that reach is capacity: with the extension fitted, the LX Desk Monitor Arm drops to 18 lb / 8.1 kg and the LX Wall Arm to 20 lb / 9.1 kg. An extension solves reach, not load, and it makes weight compatibility more restrictive rather than neutral.

The general rule follows from both. Every part you add between the arm and the monitor — adapter plate, quick-release bracket, spacers, even a heavy monitor light bar or webcam — becomes part of the mounted load. BenQ instructs owners to include peripheral weight such as a webcam or monitor light when checking capacity. If an arm that used to hold position starts to sag after you added a part, the part is the first suspect, and the arithmetic is the explanation.

Pole, Collar and Base Parts Are Ecosystem-Specific

The monitor end of a monitor arm is standardised; the desk end and the pole are not. Once you move from the VESA interface to the parts that attach to the base, the pole or the arm segment, you are in manufacturer-specific territory. Ergotron's own compatibility lists and Duronic's spare-parts catalogue both confirm it: an accessory for one arm family frequently does not transfer to another brand's pole, even though both arms share the same 75×75 and 100×100 monitor interface.

That matters for two common symptoms. If the arm slides down its vertical pole, the cause is usually a loose or incorrect pole collar or set screw — the fix is to retighten the correct collar or set screw, and to use the OEM collar rather than a generic ring that happens to fit the diameter. If the base rotates on the desk despite being tightened, the cause is insufficient clamp friction or a missing anti-rotation fitting, and the answer is the correct clamp or grommet hardware for that arm, plus any anti-rotation screws the model provides.

Tension and hinge fasteners fall into the same category. Manufacturers document how to adjust tension, but they do not sell the internal tension screw or tilt bolt as a universal replacement part. A stripped or persistently slipping tension mechanism is an OEM support or RMA case, not a hardware-store bolt substitution. If you cannot identify the exact part for your arm family, the monitor arm desk mounts guide covers how clamp and grommet bases differ and where an OEM part is the only safe replacement.

Cable Routing Through the Full Range of Motion

The cable hardware on a monitor arm — the clips that snap into the arm's extrusion, the channels beneath the forearm — exists for a moving assembly, not a static one. The routing has to keep up with the arm through its full travel: full rotation, full extension, full height adjustment. A cable that is tidy at rest can be under tension at the far end of the arm's range.

Two symptoms point here. If a cable catches or tightens when the arm extends, the routing lacks slack; the fix is to re-route the cable with an articulated loop that accommodates the movement. Areswing explicitly warns users to leave enough cable slack for full rotation, and Ergotron routes its cables through channels beneath the arm for the same reason. If a plastic cable clip breaks repeatedly, the more likely cause is a bundle that is too thick for the channel or a run that is tensioned at full extension — not a weak clip. The remedy is an OEM clip or channel, an external hook-and-loop route, or a lighter bundle.

Standalone replacement clips have no cross-brand standard. A clip that snaps into one arm's extrusion is specific to that arm; external hook-and-loop straps are more universal, but they are not equivalent to the original moulded clip. For the desk-side half of the problem — the bundle that leaves the arm and runs to the wall — the under-desk cable management guide covers trays, raceways and routing order.

Frequently Asked Questions

Conclusion

Most monitor-arm problems are not the arm. They are one of four things: a tension adjustment applied to the wrong joint, a screw of the wrong length, a plate that cannot clear a recess, or a desk interface that needs spreading or a different mounting method. Take the measurement first — which joint is moving, what pattern the monitor uses, how deep the recess is, what the desk underside looks like — and the correct part usually becomes obvious before you buy anything.

The parts divide cleanly. Screws are standardised at the monitor end: M4 for 75×75 and 100×100, with length set by the monitor's manual and changed by every spacer, washer and adapter you add. Plates are diagnostic tools for the desk side: they spread clamp load and cannot repair a weak top. Adapters and extensions convert geometry and add mass, and they never raise an arm's capacity — several officially reduce it. Grommet and pole hardware stays ecosystem-specific, which is why the exact manual beats a generic listing every time.

If the arm still will not hold position after correct adjustment, stop tightening. That is a load problem or a mechanism problem, and manufacturer service is the honest answer. When you are ready to replace or upgrade, the best monitor arms roundup sorts current models by screen size and load, the Ergotron model guide explains the LX and HX families these accessories belong to, the wobbly monitor stand fix guide covers the desk-side diagnoses in more depth, and our dual monitor arm picks cover the two-screen case where load math gets stricter. Whichever arm you run, keep the manual — it is the only document that names the correct screw for your monitor.