Mercury MerCruiser Lockwasher 5/16-24 (0.312-24) 39107
Free returns on all eligible orders
You have 30 days to request a return. All sale items are final sale.
Mercury MerCruiser Lockwasher — 5/16-24 (0.312-24) / 39107
| Field | Detail |
|---|---|
| Part Number | 39107 / 13-39107 |
| Brand | Mercury Marine / MerCruiser |
| Official Product Type | Lockwasher — OEM Marine Hardware |
| Thread / Size Spec | 0.312-24 (5/16 inch diameter, 24 threads per inch — fine thread) |
| Supersedes | None on record |
| Replaced By | No supersession confirmed — 39107 remains an active Mercury part |
| System | Hardware / Fasteners — used where the Mercury parts diagram specifies this lockwasher |
| Sold As | Individually — confirm quantity required from your parts diagram |
| Weight (approx.) | 0.02 kg / 0.7 oz |
What This Part Does
The 39107 is a genuine Mercury OEM lockwasher sized to the 5/16-24 fine-thread specification (0.312 in. diameter, 24 threads per inch). Lockwashers are used under fastener heads or nuts at positions where vibration, heat cycling, or operational loads could cause fastener loosening. Using the OEM-specified lockwasher ensures the correct fit, material grade, and locking tension for the assembly shown in the Mercury parts diagram.
Compatible Applications
- Mercury MerCruiser engine, sterndrive, and marine assembly positions where the factory parts diagram specifies part number 39107 / 13-39107
Confirm fitment using the specific Mercury parts diagram for your engine or drive model and serial number. The 0.312-24 spec identifies the thread diameter and pitch — verify this matches the fastener and mating thread at the installation position before ordering.
Serial Number & Fitment Notice
Confirm the assembly, engine model, and serial number against the applicable Mercury parts diagram before ordering. Mercury uses multiple lockwasher sizes across engine and drive assemblies — confirm 39107 is specified at the exact fastener position in your diagram.
Dimensions
- Thread spec: 0.312-24 (5/16 in. diameter × 24 TPI, fine thread)
- Exact inside diameter, outside diameter, and thickness per Mercury OEM specification — confirm against diagram for your application
When to Replace
- Lockwasher is deformed, flattened, or cracked
- Locking tabs or serrations are worn smooth
- Signs of corrosion, pitting, or stress damage
- Fastener is being removed and reinstalled as part of a service procedure — replace as a matter of course
- Mercury service procedure specifies new hardware on reassembly
OEM lockwashers should generally not be reused after removal in assemblies where fastener retention is critical to safe operation.
Service Interval
No fixed replacement interval applies. Replace whenever the associated fastener is removed during service, or whenever the lockwasher shows deformation, corrosion, or loss of locking function. Follow the applicable Mercury service manual for torque specifications at the installation position.
Installation Notes
- Confirm the fastener thread spec (5/16-24 fine thread) matches the installation position
- Place the lockwasher between the fastener head or nut and the mating surface as shown in the Mercury diagram
- Do not reuse a lockwasher that has been compressed, deformed, or corroded
- Follow Mercury’s specified torque value for the fastener at this position
- Inspect the mating thread and fastener condition before reassembly
Alternate & Superseded Part Numbers
- 39107 — Mercury / MerCruiser OEM number
- 13-39107 — Mercury catalog prefix format
No superseding number is confirmed. 39107 remains listed as an active Mercury part.
Technical FAQ
Q: What does 0.312-24 mean?
A: It is the thread specification for the fastener this lockwasher is designed for — 0.312 inches (5/16 in.) in diameter with 24 threads per inch (fine thread). Confirm this matches the fastener at your installation position before ordering.
Q: Do I need to replace this lockwasher every time I remove the fastener?
A: As a general practice, yes — especially in assemblies where fastener retention is safety-critical. A lockwasher that has been fully compressed once may not provide the same locking tension when reinstalled. At $2–3 each, replacement is inexpensive insurance on a rebuilt assembly.
Q: Can I use a generic 5/16-24 lockwasher instead?
A: Only if it matches the OEM material grade and dimensions specified for the installation. Mercury OEM hardware is manufactured to specific material and dimensional standards. When in doubt, use the OEM part number to ensure correct fit.
Q: How many do I need?
A: Check the quantity shown in the Mercury parts diagram for your specific assembly — this listing is sold individually. Order the quantity indicated in the diagram.
Parts Desk Insights
Lockwashers like 39107 are the kind of part customers often forget to order until they’re mid-service with the fastener already out. The best time to order this is before the assembly comes apart — check the diagram for the quantity required and order them with the primary service parts. The main thing to confirm is that the 0.312-24 fine-thread spec matches the fastener at the installation position, as Mercury uses several different lockwasher sizes across engine and drive assemblies and they can look nearly identical.
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
Returns & Satisfaction Guarantee
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.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.