A propeller hub is one of the hardest-working components in any high-performance drivetrain. Every launch, hard acceleration, high-speed pass, and rough-water impact transfers thousands of pounds of torque through the hub before it reaches the propeller.
Choosing the correct hub kit not only improves power transfer but also helps protect the gearcase, propshaft, and propeller from damaging shock loads.
Buckshot Racing #77 offers two premium hub kits for Mercury Racing and heavy-duty MerCruiser applications equipped with the 1.25-inch (1-1/4") fat propshaft.
Option 1 – Turning Point Hub Kit (621)
The Turning Point Hub Kit (621) is designed for boaters looking for maximum holding power and durability. This kit features larger, heavier-duty rubber cushions that provide a tighter interference fit inside the propeller barrel. The increased rubber volume offers excellent shock absorption while reducing hub movement under heavy acceleration and repeated high-RPM operation.
This hub is an excellent choice for high-horsepower lake boats, offshore performance boats, poker run boats, and performance applications where aggressive launches and repeated wide-open-throttle operation place additional stress on the hub assembly.
Option 2 – Buckshot / Mercury Racing Hub Kit (840389K06-77)
The Buckshot Racing #77 Hub Kit (840389K06-77) is a direct replacement for the factory Mercury Racing Flo-Torq hub system. It replaces Mercury OEM 840389K06 and 8M0183487 while maintaining the original factory design and installation procedure.
Each kit includes OEM-style hardware, including the thrust washer, spring washer, flat washer, brass Nyloc prop nut, and cushioned hub, making it the ideal replacement when restoring factory performance or replacing worn hub components.
Designed for Mercury Racing Fat Shaft Applications
Both hub kits fit Mercury Racing and MerCruiser applications using the 1.25-inch fat propshaft with Flo-Torq square-hub propellers.
Popular applications include Mercury Racing 260 EFI, 280 ROS, 300 Drag, 300 Pro Max, 300X, 300XS, 250R, 300R, 400R, 450R, Pro XS, Verado, and Optimax outboards equipped with SportMaster or TorqueMaster gearcases.
They also fit numerous Fleetmaster and Verado 5.25-inch gearcases, along with MerCruiser Bravo One XR and Bravo One XZ sterndrives using the 1.25-inch fat shaft configuration.
These hub kits do not fit standard 1.00-inch small-shaft propeller applications.
Improved Power Transfer and Reduced Vibration
Both hub systems are engineered to efficiently transfer engine torque while isolating the drivetrain from damaging shock loads. The cushioned hub absorbs sudden impacts generated during shifting, hard acceleration, propeller ventilation, and rough-water operation, helping reduce vibration while protecting expensive gearcases and propellers.
Proper hub engagement also minimizes chatter, reduces spline wear, and delivers smoother throttle response throughout the RPM range.
Easy Installation
Installation is straightforward using the factory Flo-Torq assembly procedure. Inspect and clean the propshaft, lightly lubricate the splines with marine grease, install the thrust washer, hub components, propeller, spring washer, finishing washer, and brass Nyloc prop nut in the correct order, then torque the prop nut to Mercury's published specification for your engine or sterndrive.
After the first outing, recheck prop nut torque to ensure the assembly has fully seated.
Buckshot Racing #77 Tech Tip
If you're replacing a worn Mercury factory hub and want an OEM-style replacement, choose the Buckshot / Mercury Racing Hub Kit (840389K06-77). If you're running high horsepower, surfacing propellers, aggressive acceleration, or simply want a tighter-fitting hub with larger rubber cushions, the Turning Point Hub Kit (621) offers increased durability and improved load distribution while maintaining smooth operation.
Replaces Mercury OEM Part Numbers
The Buckshot Racing #77 Hub Kit directly replaces numerous Mercury and Quicksilver part numbers, including: 840389A1, 840389A2, 840389A5, 840389K5, 840389K06, 840389Q06, 12-840383A2, and 8M0183487.
Final Thoughts
Whether you're restoring a factory Mercury Racing setup or upgrading to a tighter, heavy-duty hub, Buckshot Racing #77 offers the right solution for your 1.25-inch fat shaft application.
Choose the Turning Point Hub Kit (621) for maximum durability and larger rubber cushions, or select the Buckshot / Mercury Racing Hub Kit (840389K06-77) for a direct OEM replacement with factory-style hardware.
Either option delivers reliable power transfer, smoother operation, and the confidence needed for today's high-horsepower Mercury Racing and MerCruiser platforms.
Contact Mike Hill at +1-714-697-1716 or email mike@buckshotracing77.com for technical support.