Lower Unit Oil Drain Plug Screw Kit – Fits Mercury/MerCruiser Outboard & Sterndrive (Replaces 79953Q04, 816610A1)

Lower Unit Oil Drain Plug Screw Kit – Fits Mercury/MerCruiser Outboard & Sterndrive

This lower unit oil drain and fill plug screw kit is designed for a wide range of Mercury/MerCruiser applications, including Alpha One (Gen II, I, R, MR) and TR/TRS sterndrives. It also fits all Mercury outboard models that use a 3/8"-16 non-magnetic drain/fill screw.

This kit serves as a direct replacement for multiple OEM and aftermarket part numbers, including Mercury/MerCruiser 79953Q04, 816610A1, Sierra 18-2244, and Johnson/Evinrude 307552.

• Complete Kit: Includes two non-magnetic drain plug screws and two yellow gaskets.
• Material: Constructed from non-magnetic metal to meet OEM specifications.
• Thread Size: Features a standard 3/8"-16 UNC thread for a secure fit.

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.

For Johnson/Evinrude owners, here’s a guide to help you identify your engine’s serial/model: Johnson Serial Number Guide.

Confirm your engine model/year in the table below.

Technical Specifications

Package Contents

• 2 x Drain Plug Screw (Non-magnetic)
• 2 x Drain Plug Gasket (Yellow)

Installation Guide

These plugs are used for lower unit gear oil drain and fill holes. To change your gear oil:

1. Remove the top (vent) plug first.
2. Remove the bottom (drain) plug to allow the old oil to drain completely.
3. Pump new gear lube through the bottom hole until it begins to flow out of the top vent hole.
4. Quickly replace the top plug first, and then the bottom plug to minimize oil loss.
5. Ensure both plugs are torqued properly to create a secure seal and prevent leaks.

Troubleshooting & FAQ

Q: How do I know if this drain plug set will fit my engine?

A: This kit is compatible with all Mercury/MerCruiser sterndrives and outboards that use a 3/8-16 non-magnetic drain/fill screw. It also fits certain Johnson/Evinrude and Chrysler/Force models. Please review the detailed "Compatible Engine Models" and "Part Number Cross-Reference" tables on this page to confirm a match.

Q: What is the thread size of these screws?

A: The thread size is 3/8-16 UNC. It is critical to ensure this matches your gearcase housing's threads before attempting installation.

Q: Are these drain plugs magnetic or non-magnetic?

A: These are non-magnetic drain plugs. This is per the OEM specification for these applications, designed to prevent metallic shavings from being attracted to the plug and potentially damaging the threads upon removal or installation.

Q: How many plugs and gaskets are in one package?

A: Each package contains two drain plug screws and two gaskets, providing everything needed for a complete service of both the upper vent and lower drain holes on one gearcase.

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.