48-77348A45 Mercury Black Max 12 3/4 x 21 Aluminium Propeller – RH 15 Spline | Genuine Used Part

🔧 Product Description

Genuine Mercury Black Max 12 3/4 x 21 Aluminium Propeller - Part Number: 48-77348A45

A genuine used Mercury Black Max three-blade right-hand aluminium propeller for compatible Mercury and Mariner 15-spline 4 1/4-inch gearcases.

The 21-inch pitch is a high-pitch option for lighter, faster hulls capable of carrying the load while keeping engine speed within the manufacturer's wide-open-throttle range.

⚙️ Key Features

• Genuine Mercury / Quicksilver Black Max propeller
• 12 3/4-inch diameter x 21-inch pitch
• Three-blade aluminium construction
• Right-hand rotation with 15-tooth shaft application
• Flo-Torq hub-system service configuration

🚤 Compatibility

Commonly used on

• Mercury and Mariner 4 1/4-inch gearcases with 15-tooth propeller shafts
• High-pitch recreational applications selected by boat speed, load and engine RPM

Typically suits

• Engine models:
• Mercury / Mariner 40HP, 50HP and 60HP BigFoot / Command Thrust - all production years using the 4 1/4-inch gearcase
• Mercury / Mariner 70HP applications using the compatible 15-spline gearcase
• Mercury / Mariner 75HP and 80HP - 1978 onward
• Mercury / Mariner 90HP two-stroke, four-stroke and OptiMax with the 4 1/4-inch gearcase
• Mercury / Mariner 100HP and 115HP with the compatible 15-spline gearcase
• Mercury / Mariner 125HP two-stroke
• Mercury 75HP-115HP OptiMax where the recommended Flo-Torq III or equivalent hub system is fitted
• Fitment is controlled by the 4 1/4-inch gearcase, 15-tooth shaft, propeller clearance and wide-open-throttle RPM
• HP Range: 40HP Command Thrust - 125HP
• Engine Type: Mercury / Mariner two-stroke and four-stroke outboard with 4 1/4-inch 15-spline gearcase
• Year Range: Approximately 1978 onward

🔌 Function

The propeller converts engine power into thrust. The 21-inch pitch moves farther forward per revolution than lower-pitch options and is suited to hulls that can carry the pitch without lugging the engine.

⚠️ Common Signs of Failure

• Blades are bent, chipped, cracked or out of track
• The rubber hub slips and engine RPM rises without matching boat speed
• Propeller vibration increases with engine speed
• Cavitation, ventilation or poor acceleration develops after impact damage
• Hub splines, thrust faces or retaining surfaces are worn or corroded

🔄 Supersession & Cross Reference

OEM Supersession Chain

• 48-77348A45 → Replaces 48-77348A40 and 48-77348A4

OEM / Related Numbers

• 48-77348A4
• 48-77348A40
• 48-77348A45
• 835257K9 recommended Flo-Torq III hub kit for designated applications

Aftermarket / Verified Equivalents

• Michigan Wheel Match: 031044 - 12 3/4 x 21 aluminium equivalent
• Boatman / aftermarket direct 12 3/4 x 21 aluminium replacements for 48-77348A45
• Solas Amita 3 / Rubex 3 - 21-pitch aluminium alternatives with the correct Mercury 15-spline hub
• Mercury Laser II 48-16992A46 - related 21-pitch stainless-steel performance alternative

📦 Condition

• Genuine used part
• Removed from running engine where applicable
• In good working condition unless otherwise stated