Mercury MerCruiser Quicksilver 20739 Jam Nut — 3/4"-16, 5-Pack
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Mercury MerCruiser Quicksilver 20739 — Jam Nut, 3/4"-16, 5-Pack
| Part Number | 20739 |
|---|---|
| Service Format | 11-20739 |
| SKU | 20739 |
| Brand | Mercury / Quicksilver (OEM) |
| Product Type | Jam Nut |
| Thread | 3/4"-16 (UNF) |
| Package Quantity | 5 nuts |
| Supersedes | 97531 |
| GTIN | 745061130142 |
| Weight | approx. 21 g (0.75 oz) per 5-pack |
Overview
Mercury Quicksilver 20739 is a genuine OEM 3/4"-16 jam nut used across a range of Mercury and MerCruiser assemblies, including engine and transmission mounting systems, Hurth transmission mounting arrangements, Bravo gear-housing assemblies, and selected cross-shaft and steering hardware. This listing is supplied as a 5-pack — practical for service work where multiple matching OEM nuts are needed in one job, or to keep spares on hand for boats in regular saltwater service.
Important: Because 20739 appears in several different Mercury assemblies, fitment should always be confirmed by the exact parts diagram for your engine, drive, transmission, or steering system. The thread specification is 3/4"-16, but the diagram must call for 20739 / 11-20739 specifically before ordering.
Supersession
- Current part number: 20739 (service format: 11-20739)
- Supersedes: 97531
- If your service records show 97531, 20739 is the correct current OEM replacement.
Compatible Applications
- MerCruiser engine and transmission mounting systems — where parts diagram specifies 20739
- MerCruiser Hurth transmission mounting arrangements — where parts diagram specifies 20739
- MerCruiser Bravo gear-housing assemblies — where parts diagram specifies 20739
- Selected MerCruiser cross-shaft and steering assemblies — where parts diagram specifies 20739
- Various MerCruiser gasoline and diesel applications — where parts diagram specifies 20739 / 11-20739
- Always confirm by the exact parts diagram for your engine model, serial number, and assembly — 20739 appears in multiple unrelated Mercury assembly contexts
When to Replace
- Threads are damaged, corroded, or no longer engage cleanly
- Flats are rounded from previous use and cannot be reliably torqued
- Nut can no longer hold the correct adjustment or clamping position
- Significant corrosion is present, especially in saltwater environments
- During alignment or mount-height adjustment on engine or transmission mounts — inspect at this time
- Any time the fastener has been removed from a critical mounting or driveline position and reuse is uncertain
Installation Notes
- Clean and inspect the mating threads before installation — damaged threads on the stud or shaft will cause incorrect torque readings and unreliable clamping
- Mercury pairs 20739 with tab washers, lockwashers, trunnions, or mounting bases depending on the assembly — inspect related hardware at the same time
- Follow the service procedure for the exact assembly rather than applying a generic torque value — jam nut tightening method and final torque vary by application
- On mount adjustment applications, confirm engine or transmission alignment after tightening the jam nut to the final position
Technical FAQ
- What is a jam nut and how is it used? A jam nut is a thin nut tightened against another nut or component to lock a threaded position in place. In MerCruiser applications, 20739 is commonly used to lock adjustment positions on engine mounts, transmission mounts, and gear-housing assemblies — preventing the adjustment from shifting under vibration or load.
- Can I substitute a generic 3/4"-16 nut? A generic nut of the same thread may physically fit, but differences in nut thickness, material, surface treatment, and intended function (jam vs. standard hex) can affect how the assembly behaves under load. In mounting and driveline applications, using the specified Mercury OEM jam nut preserves the original hardware stack-up and adjustment geometry.
- Why buy a 5-pack? Many Mercury assemblies use 20739 in multiple positions in the same assembly group, and saltwater-exposed fasteners benefit from being replaced as a set rather than individually. The 5-pack provides enough for a full service of a mount or gearcase assembly plus spares, and it is more economical than ordering single nuts for each position.
- How do I find where 20739 is used on my specific engine? Look up your engine model and serial number in the Mercury parts catalog and search the assembly diagrams for 20739 or 11-20739. This is the most reliable way to confirm the exact position and required quantity for your application.
Parts Desk Insights
Best Use Case: The 5-pack format is the right choice for mount, transmission, gearcase, or steering service where several matching OEM nuts are needed at once, or for boats in saltwater service where fastener replacement at each service visit is good practice. This jam nut appears in enough different Mercury assembly contexts that having a few on the shelf is useful for any shop doing regular MerCruiser work.
Common Issues: The most frequent mistake is ordering a generic 3/4"-16 nut without confirming it is a jam nut (thinner than a standard hex nut). If the assembly uses a jam nut and a standard hex nut is installed instead, the locking function or clearance in the assembly may be compromised. The second common issue is not confirming the exact diagram position before ordering — 20739 appears in several unrelated Mercury assemblies, so always verify against the serial-number-based parts diagram for the specific engine or drive being serviced.
Related Products
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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