Description

The Mercury MerCruiser Quicksilver Pinion Nut 11-35921 is an OEM lower-unit gearcase fastener used to secure the pinion gear to the driveshaft in compatible Mercury outboard and MerCruiser drive assemblies. This nut helps maintain proper gear positioning and preload inside the gear housing under high torque and load.

Key Features

• Genuine Mercury/Quicksilver pinion nut
• Part number: 11-35921
• Also referenced as 35921
• Thread size: 5/8″-18 UNF fine thread
• Listed thread dimension: .625-18
• Requires 1-1/16″ wrench
• Secures pinion gear to driveshaft
• Critical lower-unit gearcase fastener

Engine & Drive Compatibility

Used across select Mercury outboards, Mercury Jet applications, and MerCruiser sterndrive gear housings. Commonly associated with mid-to-high horsepower Mercury 2-stroke outboards, including 40 HP through 300 HP applications, select 45/50/60/100/115 HP configurations, V6 Black Max, XR2, XR4, XR6, Pro Max models, and Mercury 45 Jet, 55 Jet, 105 Jet, and 110 Jet assemblies.

Serial Number Fitment Notice

Verify fitment by engine or drive serial number, gearcase diagram, driveshaft configuration, and pinion gear assembly before ordering. Pinion hardware can vary by gearcase family, shaft size, gear ratio, and production range.

When This Part Needs Replacement

Replace this pinion nut during lower-unit rebuilds, driveshaft removal, pinion gear service, gearset replacement, or anytime the original nut has been removed, damaged, rounded, corroded, or compromised.

Installation Notes

Pinion nut service requires proper lower-unit disassembly tools and Mercury service procedures. Do not reuse a worn or previously stressed locking nut in critical gearcase service. Confirm gear preload, backlash, shim setup, and contact pattern during reassembly.

Alternate/Superseded Part Numbers

Primary Mercury references: 11-35921 and 35921. Common aftermarket interchanges include Sierra Marine 18-3718, Sierra Marine 18-3719, GLM Products 11190, and Recmar REC11-35921.

Parts Desk Insight

The pinion nut is buried inside the gearcase, but it is not a throwaway detail. Replacing it during gearcase service helps protect the gearset from movement, preload issues, and expensive repeat teardown.

Shipping: Ships same or next day for fast Canada wide shipping.