Mercury Quicksilver Hex Head Cap Screw 10-34353 | 3/8"-16 x 1" OEM MerCruiser Engine Fastener

OEM 3/8"-16 x 1" Hex Head Cap Screw for MerCruiser Engines

The Mercury Quicksilver 10-34353 is a genuine OEM hex head cap screw called out across a wide range of MerCruiser engine, bracket, pump, pulley, and accessory mounting locations. At 3/8"-16 coarse thread and 1.00" in length, it is a precision-grade fastener specified for locations where a generic hardware-store substitute is not appropriate.

When the Mercury parts diagram calls for this number, this is the correct screw. MerCruiser uses similar 3/8"-16 screws in multiple lengths, coatings, and strength grades across the same engine — a screw that looks identical may be 1/4" longer or shorter, which matters in blind holes and clamped assemblies.

Part Information

• Part Number: 10-34353
• Short Reference: 34353
• Brand: Mercury / Quicksilver
• Official Product Type: Hex Head Cap Screw
• Thread Size: 3/8"-16 UNC (coarse thread)
• Length: 1.00"
• Head Style: Hex head
• Supersedes: F1867, F2202 (earlier factory references — verify by diagram)
• Approximate Weight: 15 g

Compatible Applications

• MerCruiser MCM 120 / 140 / 2.5L / 3.0L inline-4 – bracket and accessory mounting locations per diagram
• MerCruiser 4.3L / 4.3LX / 4.3LH V6 – bracket and pump mounting locations per diagram
• MerCruiser 5.0L / 5.7L / 350 MAG / 350 MAG MPI small-block V8 – accessory and pulley mounting per diagram
• MerCruiser 330 HP / 340 MIE / 370 TRS / 400 TRS / 454 MAG MPI big-block – where diagram specifies
• MerCruiser D7.3L D-Tronic 300 diesel – where diagram specifies
• Alpha and Bravo engine package accessory mounting locations – where diagram specifies

Fitment Note: Always confirm fitment by engine serial number and parts diagram position before ordering. This screw appears across many diagram locations — the diagram is the definitive reference for the correct length and grade at each specific location.

System & Diagram Position

This screw appears in multiple sections of the MerCruiser parts diagram depending on the engine model. Common diagram locations include:

• Seawater pump mounting – see Mercury MerCruiser Seawater Pump Kit 8M0139995
• Seawater pump pulley mounting – see Mercury MerCruiser Seawater Pump Pulley 8M0150724
• Serpentine belt and pulley assemblies – see Mercury MerCruiser Serpentine Belt & Pulley Kit 8M0150824
• Alternator, power steering pump, and accessory drive bracket mounting
• Engine-mounted sensor and accessory brackets

Dimensions

• Thread: 3/8"-16 UNC coarse thread
• Length: 1.00" (under head)
• Head Style: Hex head cap screw
• Wrench Size: Standard 9/16" hex

When to Replace

• Original screw is missing, seized, or corroded
• Threads are stripped, cross-threaded, or the screw no longer clamps securely
• Head is rounded or damaged and cannot be properly torqued
• Incorrect hardware was previously installed at this location
• Any time the assembly is disassembled and the screw shows wear or corrosion

Installation Notes

• Verify mounting hole threads are clean and undamaged before installation
• Compare the removed fastener to the replacement for thread pitch, length, and head style before installing
• Torque to the specification in the Mercury service manual for the exact assembly location — torque varies by location
• Do not substitute a longer screw in blind holes — it can bottom out before the component is properly clamped
• Apply thread-locking compound only where specified by the Mercury service manual for this location

Related Parts

• Mercury MerCruiser Seawater Pump Kit 8M0139995
• Mercury MerCruiser Seawater Pump Gasket 27-34897 – Pack of 2
• Mercury MerCruiser Seawater Pump Pulley 8M0150724
• Mercury MerCruiser Sea Pump Pulley 8M0141645
• Mercury MerCruiser Serpentine Belt & Pulley Kit 8M0150824
• Mercury MerCruiser Power Steering Pump Pulley 8M0150723
• Mercury MerCruiser Quicksilver Serpentine Belt 865615010

Technical FAQ

Q: Can I use a standard hardware-store 3/8"-16 x 1" bolt instead?
A: Not recommended for OEM-specified locations. Mercury OEM fasteners are made to specific strength grades, coatings, and dimensional tolerances for the application. A generic bolt may look identical but differ in tensile strength, corrosion resistance, or head geometry in ways that matter in marine engine environments.

Q: What is the difference between 10-34353 and other 3/8"-16 MerCruiser screws?
A: Length, coating, and strength grade. MerCruiser uses multiple 3/8"-16 screws across the same engine in different lengths (3/4", 1", 1-1/4", etc.). Always match by part number and diagram position, not just thread size.

Q: What do the superseded numbers F1867 and F2202 mean?
A: These are earlier Mercury factory reference numbers for the same fastener. If you have an older parts list showing either of these numbers, 10-34353 is the current OEM replacement. Verify against the current diagram for your engine serial number.

Q: How many of these screws does my engine require?
A: The quantity varies by engine model and the number of locations where this screw appears in the diagram. Check the Mercury parts diagram for your specific engine serial number to confirm the total quantity at each location before ordering.

Parts Desk Insights

Best use case: This screw is the right call when you have a Mercury parts diagram that specifically calls for 10-34353 and you need an exact OEM replacement — most commonly during seawater pump service, pulley assembly work, and accessory bracket replacement on small-block and big-block MerCruiser engines.

Common issues: The most frequent issue is ordering by thread size alone. MerCruiser uses similar 3/8"-16 screws in multiple lengths across the same engine — a screw that looks identical may be 1/4" longer or shorter, which matters in blind holes and clamped assemblies. Always match by part number and diagram position. A second common issue is ordering only one when the diagram calls for multiple at the same location — check the diagram for your engine before ordering to confirm the full quantity needed.