High-performance Mercury Racing outboard engines require hardware that maintains structural integrity under extreme conditions. Fasteners in critical steering and tiller-arm–to–one-piece exhaust tuner plate assemblies must withstand high tensile loads, repeated torque cycles, and constant exposure to water and atmospheric corrosion.
The 4-piece Socket Head Bolts and Mil-Spec Washers Kit from Buckshot Racing #77 is designed to provide mechanical reliability and environmental durability that meet or exceed the requirements of these applications. This hardware serves as a direct replacement for Mercury screw part number 10-132121 (132121) and washer part number 12-816056 (1816056) used on Mercury Racing 2.5-liter engines with both short 15" and standard 20" mid-sections.
Alloy Socket Head Cap Screws
The socket screws in this kit allow for easy installation. They are manufactured from alloy steel with a tensile strength of 170,000 psi. This strength exceeds the 150,000 psi specification associated with conventional Grade 8 fasteners, ensuring secure clamp load under demanding operating conditions. The socket head design enables precise torque application and provides accessibility in confined clamp bracket assemblies.
Zinc-Flake Coating
To improve corrosion resistance, each screw is finished with a zinc-flake coating. Independent testing indicates this coating provides approximately twenty times (20x) the corrosion resistance of conventional zinc-plated finishes and offers performance comparable to Dacromet coatings commonly used in industrial and marine service. This protection helps the screws maintain structural integrity in both saltwater and freshwater environments.
Mil-Spec Washers
The washers are produced from 312 stainless steel and are manufactured to conform to U.S. military specifications for material and dimensional accuracy. This ensures uniform strength, hardness, and corrosion resistance. Dimensional specifications are an inside diameter of 0.515", an outside diameter of 0.875", and a thickness range of 0.030–0.033".
The washers distribute the load across the mounting surface while allowing for more precise torque.
Application and Fitment
This hardware directly replaces Mercury’s OEM screw and washer specified under part numbers 10-132121 (132121) and 12-816056 (1816056). It is used in tiller-arm and swivel-bracket assemblies across a range of Mercury Hi-Perf outboards, including the 225X EFI Promax, 2.5L EFI and EFI Offshore engines, the 200 HP XS 6-cylinder 2.5L in both standard and ROS versions, the 225 EFI Pro Max and Super Mag, the 245 HP Carb, the 260 EFI, the 280 ROS, and the 300 Drag.
Pricing Reference
Based on published manufacturer-suggested retail pricing, Mercury screws are listed at $29.11 each and washers at $5.09 each. A full set of two screws and two washers totals $68.40.
This four-piece tiller-arm bolt kit combines 170,000 psi alloy-steel socket head cap screws with zinc-flake corrosion protection and 312 stainless steel washers built to military specifications.
The components replace Mercury OEM part numbers 10-132121 and 12-816056 across multiple outboard engine models. With enhanced tensile strength, superior corrosion resistance, and adherence to mil-spec standards, the kit offers a technically robust solution for steering and tiller-arm assemblies operating in demanding marine environments.
For technical support, contact Mike Hill at +1-714-697-1716 or mike@buckshotracing77.com.