Mercury Bravo III Front Propeller Nut 859131 – Superseded by 8M0105210

Mercury Bravo III Front Propeller Nut 859131

Part Number: 859131
Brand: Mercury Marine
Official Product Type: Front Propeller Nut
System: Bravo Sterndrive Propeller Hardware Stack
Condition: New OEM

Supersession Notice

Part number 859131 has been superseded by 8M0105210 as the current Mercury OEM replacement. If you are ordering new stock, the 8M0105210 is the current part. The 859131 may still be available while supplies last and is interchangeable with the current number.

Additional cross-reference numbers associated with this Bravo III prop nut family: 805092T and 805092.

What It Does

The Mercury 859131 is the genuine OEM front propeller nut used in the Bravo III sterndrive propeller hardware stack. On Bravo III drives, which use a counter-rotating dual-propeller system, the propeller hardware stack includes separate front and rear nuts — this is the front nut, which installs after the front propeller and secures it in position before the remaining hardware is assembled. Using the correct OEM nut ensures proper thread engagement, correct torque retention, and compatibility with the Bravo III propeller stack geometry.

Compatible Applications

• MerCruiser Bravo III sterndrive — front propeller nut position
• MerCruiser Bravo One sterndrive — verify by serial number and parts diagram
• MerCruiser Bravo Two sterndrive — verify by serial number and parts diagram
• MerCruiser Bravo X and Bravo XR high-performance sterndrives — verify by serial number
• Zeus 3000 pod drive — verify by serial number and parts diagram

Serial Number Note: Always confirm fitment using your exact drive model and serial number in the Mercury Parts Catalog. Bravo III uses separate front and rear propeller nuts — confirm you are ordering the correct position (front) before purchasing.

Diagram Position

This nut occupies the front prop nut position in the Bravo III propeller hardware stack diagram. It installs after the front propeller and before the remaining rear propeller hardware. Do not confuse with the rear propeller nut, which is a separate part.

Supersedes / Alternate Part Numbers

• 859131 — original Mercury OEM part number (this listing)
• 8M0105210 — current superseding replacement
• 805092T — earlier cross-reference number, same application family
• 805092 — earlier cross-reference number, same application family

Kit Contents

Single OEM front propeller nut. Tab washers, rear nuts, and thrust hubs are sold separately — see related products below.

Service Interval

Inspect the propeller nut every time the propeller is removed. Replace if the nut is corroded, threads are damaged, or the nut has been rounded from improper tool use. Mercury service manuals specify a torque value for Bravo III propeller hardware — always torque to spec and use the correct retention hardware for your drive.

Technical FAQ

Q: What is the difference between the front and rear propeller nut on a Bravo III?
Bravo III drives use a counter-rotating dual-propeller system with separate front and rear propellers, each secured by its own nut. The front nut (this part) secures the front propeller; the rear nut secures the rear propeller. They are not interchangeable — always confirm which position you need before ordering.

Q: Should I order 859131 or the superseding 8M0105210?
Both are interchangeable for the same application. If you need the part now and 859131 is in stock, it is a valid OEM replacement. For future orders, the 8M0105210 is the current active part number and is more likely to remain available long-term.

Q: Can I reuse the propeller nut after removing the propeller?
If the nut is in good condition with clean, undamaged threads and no corrosion, it can often be reused. However, if there is any thread damage, rounding, or corrosion, replace it. On saltwater boats, replacing propeller hardware at each service is good practice.

Related Products

• Mercury MerCruiser Propeller Nut 8M0105210 – Current Replacement for 859131
• Mercury Propeller Nut Kit 8M0056235
• Mercury Quicksilver Propeller Nut Kit 11-52707Q1
• Mercury MerCruiser Propeller Tab Washer 14-34817 – Bravo Two Sterndrive
• Mercury Propeller Wrench 15/16" 859046M3 – OEM Service Tool
• Mercury Propeller Wrench 1-1/16" 859046Q4 – OEM Service Tool

Parts Desk Insights

Best Use Case: This is the right part when you’re servicing a Bravo III drive and need to replace the front propeller nut — particularly after saltwater exposure has corroded the original, or when the nut has been rounded by an improper tool. It’s also a smart spare to keep on hand if you regularly pull Bravo III props for inspection or cleaning, since the front nut is removed every time the front propeller comes off.

Common Issues: The most frequent mistake on Bravo III prop hardware is ordering the wrong nut — front vs. rear. The two nuts look similar but are not interchangeable. Always confirm the position in the parts diagram before ordering. A second common issue is not torquing the nut to the Mercury-specified value after reinstallation — an under-torqued front prop nut can allow the propeller to shift under load, which causes vibration and accelerated wear on the propeller shaft and drive components.