Drain Screw – Fits Mercury/Mariner Outboards & MerCruiser Stern Drives (Replaces 10-79953, 10-79953A2)

Drain Screw – Fits Mercury/Mariner Outboards & MerCruiser Stern Drives

This gear case drain screw is designed for a precise fit on a wide range of outboard motors and stern drives. It is compatible with all Mercury/Mariner outboard models that use a 3/8-16 drain screw (excluding the Verado series), all MerCruiser I, R, MR, Alpha One, TR, and TRS stern drives with 3/8-16 screws, and all Chrysler/Force/US Marine models that utilize the same 3/8-16 thread size.

This part serves as a direct replacement for multiple OEM and aftermarket part numbers, including Mercury 10-79953, 10-79953A2, 10-79953Q04, 10-79953Q2, 10-20259, 10-28634, and 10-28634A1; Chrysler/Force 10-F50109 and F40109; GLM 22420; Mallory 9-72650; and Sierra 18-2244.

• Material: Constructed from high-grade, non-magnetic stainless steel for superior corrosion resistance.
• Installation: Features a hex head for easy hand tightening with a standard wrench.
• Included Hardware: Comes complete with a drain screw and three drain screw gaskets.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here’s a guide to help you identify your engine’s serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Technical Specifications

Package Contents

• 1 x Gear Case Drain Screw (Replaces 10-79953Q04)
• 3 x Drain Screw Gaskets (Replaces 26-830749)

Installation Guide

1. Position a drain pan under the gear case drain plug on your lower unit.
2. Using a large flathead screwdriver or appropriate hex wrench, carefully loosen and remove the lower drain screw.
3. Remove the upper vent screw to allow the gear lube to drain completely.
4. Once draining is complete, inspect the old gear lube for any metal shavings or milky appearance, which could indicate internal wear or water intrusion.
5. Clean the drain and vent plug areas on the gear case.
6. Install a new gasket on the new drain screw.
7. Insert the gear lube pump or filler tube into the lower drain hole and fill until lubricant exits the upper vent hole.
8. Reinstall the upper vent screw first, then quickly remove the filler and reinstall the new lower drain screw.
9. Hand-tighten both screws securely. Do not overtighten.
10. Wipe the area clean and check for leaks after running the engine.

Troubleshooting & FAQ

Q: How do I confirm this fits my engine?
A: This screw fits most Mercury, Mariner, MerCruiser, and Chrysler/Force models using a 3/8-16 drain screw. The best way to confirm is to check your service manual or compare your existing screw's part number to the cross-reference list provided. It is not compatible with Mercury Verado models.

Q: What is the benefit of a non-magnetic drain screw?
A: A non-magnetic drain screw, made of high-grade stainless steel, offers maximum corrosion resistance in marine environments. Some drain screws are magnetic to capture metallic debris, but this design prioritizes durability and preventing galvanic corrosion.

Q: Why are three gaskets included?
A: Drain screw gaskets are single-use items and should be replaced every time the gear lube is changed to ensure a proper seal and prevent leaks. We include three gaskets so you have spares for future services.

Q: OEM vs. Aftermarket?
A: This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

Q: How fast do you ship and how much does it cost?
A: We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

Q: What is your warranty and return policy?
A: This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.