The Multiquip 21406 O-Ring Size-16 Buna-N 90 is a genuine OEM seal designed for Whiteman ride-on power trowels including the HTX44, STX55, STXD6i, and HTXD6i series. As a direct OEM replacement, part 21406 is manufactured to the exact material grade and dimensional specification required by the original hydraulic or fluid system on these machines. Sourced directly from Multiquip, this seal integrates without modification into your trowel's existing hardware. Verified fitment covers HTX44K4, HTX44K5, HTX44Y4, HTX44Y5, STX55J6, STX55Y6, STXD6i, and HTXD6i models.
Key Features
- Buna-N 90 Durometer Compound — The 90-durometer nitrile (Buna-N) material provides firm compression resistance and strong resistance to hydraulic fluid, oil, and fuel exposure common in ride-on trowel service environments.
- Size-16 OEM Specification — Dimensioned to the exact Size-16 cross-section and inner diameter called out in the Multiquip parts system, ensuring a correct seat and seal when installed in the original groove.
- Genuine OEM Part — Supplied directly by Multiquip, part 21406 meets the same material and dimensional standards as the seal originally installed at the factory.
- Broad HTX and STX Series Fitment — Confirmed for HTX44K4, HTX44K5, HTX44Y4, HTX44Y5, STX55J6, STX55Y6, STXD6i, and HTXD6i hydrostatic ride-on trowels.
- Leak Prevention — A correctly seated O-ring maintains fluid containment in hydraulic and fluid circuits; a worn or extruded seal leads to fluid weeping, pressure loss, and potential hydraulic system damage.
An O-ring is a molded-loop seal that sits within a machined groove, compressing between two mating surfaces to prevent fluid or air from passing through the joint. On hydrostatic ride-on trowels like the HTX and STX series, O-rings are used throughout the hydraulic circuit — at fittings, valve bodies, and hydraulic motor ports — where maintaining pressure integrity is critical to blade pitch control and drive response. When an O-ring degrades, takes a permanent set, or is cut during reassembly, it can no longer maintain a full seal, resulting in fluid leakage, reduced hydraulic pressure, and inconsistent trowel performance. Replacing a worn seal with the correct Multiquip 21406 O-Ring Size-16 Buna-N 90 restores the fluid boundary and keeps the hydraulic system operating within its designed pressure range.
For questions about fitment or to confirm this is the correct part for your machine, contact the DHS Equipment team before ordering.
Part Details
| Part Number | 21406 |
|---|---|
| Brand | Multiquip |
| Part Type | Genuine OEM |
| Description | O-Ring Size-16 Buna-N 90 |
Compatibility & Fitment
| Name | Model |
|---|---|
| Whiteman Ride-On Power Trowels | HTX44K4 |
| Whiteman Ride-On Power Trowels | HTX44K5 |
| Whiteman Ride-On Power Trowels | STX55J6 |
| Whiteman Ride-On Power Trowels | HTX44Y4 |
| Whiteman Ride-On Power Trowels | HTX44Y5 |
| Whiteman Ride-On Power Trowels | STXD6i |
| Whiteman Ride-On Power Trowels | HTXD6i |
| Whiteman Ride-On Power Trowels | STX55Y6 |
Verify Before You Order
Fitment is machine-number and revision-specific; always confirm your model and serial number against the fitment list.
Why Buy From DHS Equipment
Every part is verified against the manufacturer's part number before it ships, so what you order is what arrives. We carry parts from leading OEM brands and our own DHS Quality Parts line of professional aftermarket components. Need help finding the right part? Our team is available to confirm compatibility whenever you need it. Orders are processed fast to keep your jobs on track. We don't just sell parts. We keep you jobsite ready.
Questions? Contact our team at [email protected] or 866-611-9369 — DHS Equipment is here to help you maintain peak performance.
