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Your Piaggio Fly or Derbi Boulevard deserves better than a pitted steel stalk and blurry glass. The Koeep rearview mirror set for Piaggio Fly 50/100/125/150 and Derbi Boulevard 50/100/150 4T is a direct-fit replacement pair: M8 x 1.25mm threads on both stalks, E-marked convex glass, locking nuts in the box.

Everything below sticks to published specs and the 2026 compliance picture under UN ECE Regulation No. 46 (R46) for L-category vehicles — no invented numbers. If you are outfitting more than the scooter, the Koeep auto & motorcycle parts collection puts the full catalog on one page.

Specs That Decide Fit and Legality

Thread pitch decides whether the stalk screws in. Reflective area decides whether the mirror is street legal. This pair runs an M8 x 1.25mm right-hand pitch on both left and right stalks — dual right-hand — and the oval convex glass measures about 147 x 82 mm, clearing the 7-square-inch minimum that roadworthiness rules set for L-category vehicles.

Full Specification Sheet

The compliance angle matters in 2026: Euro 5+ durability and OBD-II Stage II monitoring are now enforced across all L-category vehicles, and mirrors must hold structural integrity under the extended vibration profiles of ISO 16750-3:2026. The E-mark is what keeps the set road legal in the EU/EEA — not decoration.

Fitment Matrix: Every Model This Pair Covers

Match your model and year before ordering. All eight fitments below share the same M8x1.25 RH thread and clear the ≥ 7 in² reflective-area threshold. Piaggio coverage runs 2006–2014; Derbi coverage runs 2002–2014.

Cross-Compatible Platforms on the Same M8x1.25 Architecture

Piaggio Group runs a unified parts-bin strategy across the Fly, Vespa ET, and Derbi Boulevard lines, so the same handlebar clamp geometry appears on the Vespa ET2 50 2T, the Vespa ET4 125/150 4T, and select Piaggio Liberty models. That sharing continued through 2026 as the Group consolidated its L-category aftermarket supply chain under the Euro 5+ OBD-II Stage II architecture.

One caution for Liberty owners: some Liberty variants moved to an M10x1.25mm thread. This set is M8x1.25mm only and will not fit those clamps. Check the thread on your bike first — thirty seconds that saves a return shipment.

Engineering Notes: Why Aluminum Stems Beat Steel

Galvanic corrosion

A steel stalk clamped into an aluminum handlebar is a galvanic cell waiting for rain: two dissimilar metals, one electrolyte, corrosion at the clamp interface. Koeep machines the M8 stalk from 6063-T5 aluminum alloy to remove that dissimilar-metal pair — the same material philosophy the 2026 OEM-level Piaggio spare-parts catalogs adopted.

Vibration damping

The ABS-PC composite housing shell absorbs high-frequency oscillation in the 50–125 Hz band — the dominant harmonic range of the C442M/C443M single-cylinder at cruising RPM. That kills the mirror blur single-cylinder scooters are known for, and a stable image means you actually use the mirrors instead of squinting past them.

Mirrors and DTCs: the 2026 Diagnostic Cascade

On 2026-compliant Fly and Boulevard platforms, Piaggio PADS v4.2+ runs enhanced rationality checks across the CAN-bus 2.0B network. A loose or incorrectly torqued mirror stalk can shake the handlebar harness into an intermittent ground-loop disturbance at the cluster connector — PIN 7, chassis ground — and that disturbance shows up as spurious codes.

Loose stalks have been correlated with false-positive triggers in the P0500–P0503 range (Vehicle Speed Sensor rationality) when vibration-induced harness chafing occurs near the handlebar cluster. The documented ranges:

The fix is mechanical, not electronic. Correct lock-nut torque plus thread locker removes the vibration vector that starts the cascade. The Koeep kit ships with matched lock nuts built for exactly that spec.

Installation and Service Schedule

• Torque: M8 lock nuts at 22–25 N·m with a calibrated torque wrench.
• Thread locker: one drop of medium-strength compound (Loctite 243 or equivalent) — enough to stop vibration loosening, weak enough to service later.
• Inspection interval: every 24,000 km or 24 months, re-verify lock-nut torque.
• Replace the pair when: the convex glass delaminates, or the stem shows galvanic pitting at the clamp interface.

The durability numbers back that schedule: fatigue life above 10⁷ cycles at ±2.5g vibration amplitude — roughly 160,000 km of urban riding on the Fly platform — with projected service life of 2026–2030 under normal conditions.

Material traceability, if you need it: stem in 6063-T5 per SAE AMS 4026N / ASTM B221; ABS-PC housing rated ISO 4892-2 UV-exposure Class A; black powder coat holding an ISO 9227 salt-spray rating of at least 500 hours. Those selections match the 2026 Piaggio Group service-parts specification and surpass the OEM steel-stalk configuration in corrosion resistance and vibration damping.

Shopping for Other Bikes in the Garage

Koeep applies the same direct-fit logic beyond scooters. If a Suzuki cruiser shares your workspace, the catalog stocks black rearview mirrors for the Suzuki Boulevard C109, C50, C90, M90, M50, M109, and S40 US — and for a custom build there are chrome skull mirrors for the Suzuki Boulevard C109/C109R, M109/M109R, C90, and C50.

Consumables reward the same discipline. When you also maintain a car, the buying guide on why Denso iridium spark plugs suit the Prius C shows how to pick wear parts by specification instead of price — a habit that pays off on two wheels too.

Piaggio, Vespa, and Derbi are registered trademarks of Piaggio & C. S.p.A. Koeep is an independent aftermarket parts supplier.

Ordering, RFQ, and Fitment Support

For a single set, order the mirror pair directly from the Koeep product page and check fitment against the table above. Running a fleet or a repair shop, or hunting a variant you cannot find? Send it through the request-for-quote page and Koeep will price the batch.

Pre-purchase questions have two fast channels: support@koeep.com for detailed fitment questions, or WhatsApp when you need a quick answer mid-job.

FAQ: 2026 Troubleshooting for Fly and Boulevard Mirrors