Mercury Quicksilver OEM Trim Tab Screw 66024 | 7/16-14 × 1.75 in. Gear Housing Anode Fastener

Mercury Quicksilver OEM Trim Tab Screw — Part 66024

• Part Number: 66024
• Full Catalog Number: 10-66024
• Brand: Mercury Marine / Quicksilver (Genuine OEM)
• Official Product Type: Lower Unit & Gearcase Hardware — Trim Tab-to-Gear-Housing Screw
• System: Lower Unit — trim tab / anode mounting at the gear housing
• Diagram Position: Trim tab / anode mounting screw in Mercury Gear Housing / Propeller Shaft diagrams
• Thread Specification: .437-14 / 7/16-14
• Length: 1.75 in. (44.5 mm)
• Qty Required: 1 per applicable gear-housing assembly
• Supersedes: FI3000543 (earlier Mercury reference in applicable applications)
• GTIN / UPC: 745061073425
• Weight: approx. 0.05 kg

What It Does

The 66024 is the genuine OEM screw that secures the trim tab / anode assembly to the gear housing on a wide range of Mercury and Mariner outboard lower units. Mercury gear-housing diagrams identify this fastener specifically at the trim-tab mounting location on applicable lower units. Because Mercury used several different lower-unit and trim-tab arrangements across these horsepower ranges, 66024 should be selected by gear-housing diagram and engine serial number, not by horsepower alone. Do not substitute another 7/16-14 bolt based solely on thread diameter and pitch — the correct length and OEM application specification should also match.

Compatible Applications

Confirm fitment by engine serial number and the specific Mercury Gear Housing / Propeller Shaft diagram before ordering. Several Mercury lower units use visually similar trim-tab screws with different thread sizes or lengths.

• Mercury 35 HP — selected gear-housing configurations
• Mercury 40 HP / 400 — selected gear-housing configurations
• Mercury 45 HP / 450 — selected gear-housing configurations
• Mercury 50 HP / 500 — selected gear-housing configurations
• Mercury 50 HP 3-cylinder — selected gear-housing configurations
• Mercury 60 HP 3-cylinder — selected gear-housing configurations
• Mercury 75 HP — selected gear-housing configurations
• Mercury 90 HP — selected gear-housing configurations
• Mercury 115 HP — selected gear-housing configurations
• Mercury 135 HP V6 — selected gear-housing configurations
• Mercury 150 HP V6 — selected gear-housing configurations
• Earlier Merc 402, 500, 650, 850, 1150, and 1500 models — selected configurations
• Mariner 75 HP — selected gear-housing configurations
• Mariner 90 HP — selected gear-housing configurations
• Mariner 115 HP — selected gear-housing configurations
• Mariner 220 HP — selected gear-housing configurations
• Mercury XR-4 Magnum II — selected applications
• Mercury 30 Jet — selected gear-housing configurations

Not sure it fits? Send us your Mercury or Mariner outboard serial number before ordering.

Related Components

The following parts are commonly associated with the trim-tab mounting assembly. They are sold separately and are not included with 66024:

• 31640Q4 — Trim tab / anode assembly (applicable gear housings)
• 76214Q5 — Anode (selected later gear-housing configurations)
• 856774 — Drive-shaft-housing stud washer (related assemblies)
• 65791 — 7/16 in. housing-to-stud washer (selected applications)

Part Numbers & Supersession

• 66024 — Current Mercury Marine OEM reference
• 10-66024 — Full Mercury fastener catalog format
• FI3000543 — Earlier Mercury reference; superseded by 66024 in applicable applications

When to Replace

Replace the trim tab screw when:

• The threads are stripped or damaged
• The screw head is rounded or corroded beyond use
• Significant corrosion or galvanic pitting is present on the fastener
• The screw has become bent
• The trim tab or anode was lost because the mounting hardware worked loose
• The fastener is seized or damaged during trim-tab removal

Inspect the threaded bore in the gear housing at the same time. A new screw will not hold correctly if the housing threads are damaged or corroded — the housing threads may need to be chased or the bore repaired before refitting.

Service Interval

Inspect at each anode replacement service, which should be at minimum once per season or more frequently in saltwater or high-corrosion environments. If the trim tab / anode is being replaced (recommended when 50% consumed), remove and inspect the screw at the same time and replace it if any corrosion, thread damage, or rounding is found. Do not reuse a screw that shows signs of galvanic corrosion at the gear-housing interface.

Installation Notes

• Confirm the lower-unit diagram specifies 66024 for your exact gear-housing and trim-tab configuration before installing
• Mark the original trim-tab position before removal if it has been adjusted for steering-torque correction — the tab angle affects how the boat steers under power and the original position should be preserved unless intentionally readjusting
• Inspect the screw threads and the threaded gear-housing bore before installation — a seized or corroded bore must be addressed before fitting the new screw
• Check the trim tab / anode for excessive wear or loss of material and replace if more than 50% consumed
• Follow the applicable Mercury service-manual torque specification for the trim-tab screw — do not overtighten into the gear-housing bore

Technical FAQ

Q: Is 66024 just a standard 7/16-14 bolt?
No. While the thread diameter and pitch are 7/16-14, 66024 is the specific OEM trim-tab-to-gear-housing fastener for these Mercury and Mariner lower units. The length (1.75 in. / 44.5 mm) and OEM specification matter for correct engagement in the gear-housing bore. Do not substitute a generic hardware-store bolt without confirming the length and thread engagement match the Mercury diagram.

Q: What superseded 66024?
66024 supersedes the earlier FI3000543 reference in applicable applications. 66024 is the current Mercury OEM number to order if your parts list or service record shows FI3000543.

Q: My trim tab fell off — do I just need the screw?
If the trim tab separated because the screw backed out, also inspect the threaded bore in the gear housing for damage or corrosion — a screw that worked loose over time often indicates thread damage in the housing bore as well. Replace the screw and inspect (and replace if needed) the anode assembly at the same time. If the anode was mostly consumed, it is past its replacement interval.

Q: How do I set the trim tab position after reinstalling?
If the outboard tracked straight before and the trim tab is going back on without adjustment, mark the original position before removal and reinstall at the same angle. If the boat pulls to one side under power, the trim tab angle can be adjusted slightly to compensate. Refer to the applicable Mercury service manual for the trim-tab adjustment procedure for your engine.

Parts Desk Insights

The most common situation with 66024 is a customer who has lost their trim tab — it backed out at some point and separated from the gear housing. When that happens, the threaded hole in the housing is usually corroded or damaged, and just installing a new screw without inspecting the bore means it will likely back out again. The housing threads should be chased or inspected before refitting. The other thing to check is the trim-tab position if it had been previously adjusted for steering pull — if there is no reference mark from before removal, the boat may develop a new pull issue after reinstallation. Telling customers to mark the position before pulling the tab saves a lot of follow-up adjustments. Anodes on these engines should be checked at least once a season, and the screw should come out and be inspected each time the anode is replaced.