The Buckshot Racing #77 Mercury 15-Spline Brass Propeller Washer is a replacement component used in compatible Mercury and Mariner propeller-hub assemblies with traditional 15-spline propeller shafts and rubber-hub propellers.
 
This washer is part of the propeller retention hardware stack and works with the propeller nut and a separate tab washer to keep the propeller securely fastened during operation.
Mercury catalogs 12-31211Q03 as the current replacement for earlier 12-31211A2 and 12-31211A3 washer assemblies.
 
How the Mercury Tab-Washer System Works
 
Unlike a cotter-pin-style propeller installation, this Mercury system uses a splined washer plus a separate tab washer.
 
The splined washer installs in the propeller hardware stack and indexes with the propeller shaft. The separate tab washer, commonly Mercury 14-816629Q, is then used with the propeller nut.
 
After the nut is tightened correctly, one of the tab washer ears is bent into position against the nut to help prevent it from loosening. Mercury parts diagrams show 31211Q03 as the washer assembly and 816629Q as the separate tab washer immediately behind the propeller nut.
 
That distinction is important: 12-31211Q03 is not itself the locking tab washer.
 
Mercury 15-Spline Propeller Applications
 
This washer is used on numerous compatible Mercury and Mariner outboards with 15-spline propeller shafts and traditional rubber-hub or solid-hub propeller hardware.
Mercury application data shows 12-31211A2 / A3 / Q03 across many V6 outboard and sterndrive propeller systems, including various 135 HP, 150 HP, 175 HP and 200 HP Mercury V6 applications, Magnum-series engines, and related gearcases.
 
Mercury’s propeller guide also shows the washer used with older solid-hub stainless propellers and alongside the 14-816629Q tab washer and 11-52707Q1 propeller nut in compatible installations.
 
Fitment should always be confirmed by the original propeller hardware, gearcase, and Mercury part number rather than horsepower alone.
 
Brass Construction
 
Brass is well suited to marine propeller hardware because it resists corrosion and works well in a service environment that is repeatedly exposed to water, grease, and removal/reinstallation.
 
The washer should be inspected whenever the propeller is removed. Replace it if the splines, seating surfaces, or retaining features show excessive wear, deformation, or corrosion.
 
Buckshot Racing #77 Installation Tech Tip
 
Whenever servicing the propeller, inspect the complete hardware stack, including the forward thrust washer, propeller hub, 12-31211Q03 splined washer, 14-816629Q tab washer, and propeller nut.
 
Install the hardware in the correct order for the specific gearcase and propeller. Tighten the propeller nut to the Mercury specification for the application, then bend the appropriate tab on the locking washer into position against the nut.
 
Do not substitute a cotter pin where the factory system is designed around a tab washer.
The Buckshot Racing #77 Mercury Brass Propeller Washer replaces 12-31211Q03, 12-31211A2, and 12-31211A3 and is intended for compatible 15-spline Mercury propeller shaft and rubber-hub propeller assemblies using the traditional Mercury tab-washer locking system.