Mercury MerCruiser Quicksilver Screw (3/8-16 x 2-1/2 in.) 668631
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Product Description
Mercury 668631 is a 3/8-16 x 2-1/2-inch screw used in specified Mercury cylinder-head and MerCruiser exhaust assemblies. It appears as a cylinder-head screw in the V-225 reed-block and cylinder-head diagram and as a fastener in several MerCruiser exhaust-manifold and elbow layouts.
Key Features
- Mercury catalog number: 10-668631, also written 10-66863 1
- Thread: 3/8-16; length: 2-1/2 in.
- Replacement for earlier screw 10-66863.
Engine Compatibility & Fitment Notice
Examples include Mercury V-225 engines from serial 5628028 and the exhaust-manifold/elbow assembly on specified MerCruiser 6.2L MPI 300 engines. Confirm the exact assembly callout and fastener length before ordering; use the engine service procedure for tightening and any replacement requirements.
Alternate / Superseded Part Numbers
10-668631 supersedes 10-66863.
When This Part Needs Replacement
Replace screws with damaged threads, rounded heads or corrosion, and observe any service-manual replacement requirements for the particular joint.
Installation Notes
Use the procedure for the actual cylinder-head or exhaust assembly; its torque requirements cannot be inferred from screw size alone.
Mercury Parts Finder
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Parts Desk Insight
This part number serves both outboard and MerCruiser applications. Identify the assembly before selecting its tightening procedure.
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 1-3 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
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We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
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For return authorization, please contact our support team before shipping anything back.