Mercury MerCruiser Quicksilver Gear Housing Hex-Head Screw 65210 – 3/8"-16 x 1"

Mercury MerCruiser Quicksilver Gear Housing Hex-Head Screw 65210 – 3/8"-16 x 1"

Part Number: 65210 (Service format: 10-65210)
Brand: Mercury Marine / Quicksilver (OEM)
Type: Hex-Head Screw
Thread: 3/8"-16
Length: 1.00 in.
Supersedes: F1870
GTIN: 745061779457

Genuine Mercury Marine OEM hex-head screw used in selected Mercury outboard and MerCruiser gear housing and lower-unit assemblies. Mercury parts diagrams place this fastener in the gearcase area, where it is commonly paired with the associated lockwasher (35479) and thrust-washer hardware.

Compatible Applications

• Selected MerCruiser Alpha One Gen II gear housing assemblies
• Selected Mercury outboard gearcase assemblies — including certain 90 / 900 six-cylinder configurations
• Other Mercury and MerCruiser lower-unit applications where 65210 appears in the parts diagram
• Exact fitment must be confirmed against the correct engine or drive serial-number parts diagram

Dimensions

• Thread: 3/8"-16 UNC
• Length: 1.00 in.
• Head style: Hex head

System

Gear housing / lower-unit assembly — secures gear-housing cover or associated components at the diagram position shown in the applicable Mercury parts diagram. Commonly paired with lockwasher 35479. Refer to the Mercury parts diagram and service manual for your specific model and serial number for torque specification and exact position.

When to Replace

• Threads are damaged or stripped
• Hex head is rounded or corroded beyond re-use
• Fastener cannot be torqued correctly during gear-housing service
• Any time the gear housing is disassembled for service

Service Interval

Inspect at every gear-housing or lower-unit service. Replace if threads or the hex head show any damage. Best practice is to replace fasteners any time a gear housing is fully disassembled, particularly in saltwater environments where corrosion accelerates thread wear.

Installation Notes

• Inspect mating threads in the housing before installation
• Install with lockwasher 35479 where specified in the parts diagram
• Apply corrosion-inhibiting compound to threads per Mercury service-manual guidance for the specific assembly
• Torque to specification per the applicable Mercury or MerCruiser service manual
• Confirm part number by diagram position — do not substitute by thread size alone, as head style and plating are application-specific

Alternate & Superseded Part Numbers

• Current: 65210 / 10-65210
• Supersedes: F1870

Related Parts

• Mercury MerCruiser Alpha One Gen II Bearing Carrier Assembly 14587A7
• Mercury Quicksilver Lower Unit Seal Kit 26-33144A2 | MerCruiser IA IB IC R MR Alpha One Gen 1
• Mercury MerCruiser Quicksilver Gearcase Roller Bearing Shim Set 42637A1
• Mercury MerCruiser Quicksilver Bearing Carrier Seal 8M0204670
• MerCruiser Alpha One Gen II Zinc Anode Kit
• MerCruiser Oil Seal 14077
• Mercury MerCruiser Quicksilver Nut 8M0214936

Technical FAQ

Q: Can I use a generic 3/8"-16 x 1" bolt as a substitute?
A: Not recommended. This fastener is specified by Mercury for the gear-housing assembly and is selected for its head geometry, strength grade, and corrosion-resistant plating. A generic hardware-store bolt may differ in one or more of these properties, which can compromise the clamping arrangement in a saltwater-exposed lower unit.

Q: Do I need the lockwasher separately?
A: Yes, where the parts diagram specifies lockwasher 35479, it must be ordered separately. This listing is for the screw only.

Q: How many screws does my assembly require?
A: The quantity varies by application. Check the Mercury parts diagram for your specific drive or outboard model and serial number to confirm how many are required at your diagram position.

Q: My diagram shows F1870 — is 65210 the correct replacement?
A: Yes. Mercury Marine has superseded F1870 with the current part number 65210.

Genuine Mercury Marine / Quicksilver OEM part. Confirm fitment by part number, diagram position, and serial number before ordering.

Parts Desk Insights

Best use case: This screw is the correct fastener for gear-housing and lower-unit service on the specific Mercury or MerCruiser applications where part number 65210 appears in the parts diagram. It is a consumable fastener in any full lower-unit rebuild — best replaced rather than reused, especially on boats operated in saltwater where corrosion can compromise thread integrity over time.

Most common mistake: Substituting a generic 3/8"-16 bolt because the thread size matches. Hardware-store fasteners are not selected for marine corrosion resistance, head geometry, or the specific strength grade Mercury specifies for this position. In a gear-housing assembly that must hold up under load and saltwater exposure, the wrong fastener is a reliability risk. Always order the OEM part number.

Fitment guidance: Confirm 65210 in the parts diagram for your specific drive or outboard model and serial number before ordering. Note the quantity required — Mercury may specify multiple screws at this position depending on the application. If your diagram shows F1870, this current part is the direct OEM replacement.