SPECIAL TOOLS FOR AUTOMOTIVE REPAIR

NUMBER XZN15MMB

15mm Hinge Pin Tool for Mercruiser Mercury boat.

RARE 15MM SPECIAL SOCKET TOOL 12 POINT XZN STYLE 

Note: This tool measures 14.5mm from point to point (outer diameter). 

Hinge Pin Tool fits the screws on bell housing for Mercruiser Alpha One 

Gen I or Gen II drives, and all Mercruiser Bravo drivers. 

15mm Hinge Pin Tool (sometimes referred to as a XZN 15mm 12-point or triple-square style socket) is a special marine tool designed for Mercury Mercruiser sterndrive (outdrive) systems. It is primarily used on Alpha One, Alpha Gen II, Bravo I, II, and III units, as well as some related models.

This tool removes and installs the hinge pins (also called pivot pins or gimbal hinge pins) located on the port and starboard sides of the gimbal ring (or transom assembly). These pins connect the drive unit to the gimbal housing and allow the outdrive to tilt and trim. The hinge pins are recessed and have a unique 12-point

 (XZN-style) head that requires a precise-fitting socket to avoid stripping.

The tool is a deep socket that engages the head of the hinge pin bolt.

Note on the "15mm" designation: Many aftermarket or custom versions are labeled as 15mm because that's the approximate measurement across the points or flats of the fastener it fits. The official Mercury part (91-78310) and its equivalents are engineered specifically for this application rather than a standard metric socket. 

A regular 15mm 12-point socket may be close but often doesn't fit perfectly and can round off the fastener. 

Why You Need It?

Hinge pins must be removed during common maintenance jobs on Mercruiser boats, such as:Replacing U-joint bellows, exhaust bellows, or shift cable bellows.

Servicing the gimbal bearing.

Removing/reinstalling the entire outdrive unit.

Replacing the hinge pins themselves if they are corroded or damaged.

These pins often seize due to corrosion (especially in saltwater), so the tool is frequently paired with penetrating oil, heat (e.g., MAPP gas torch), and sometimes a slide hammer or impact methods.

Compatible Part Numbers

Mercury/Quicksilver OEM: 91-78310

Sierra (aftermarket): 18-9861

This tool is specifically manufactured for the right fit. 

Overall length of this tool is 2 inches and the drive size is 1/2 inch. 

Tips for Use

• Apply penetrating oil (e.g., PB Blaster) and let it soak, sometimes for days on stubborn pins.
• Use a long breaker bar for leverage; avoid cheap impact tools that can damage the splines.
• Some mechanics weld a nut onto the tool or use vise grips for extra hold on very stuck pins.
• When reinstalling, apply Loctite (threadlocker) and torque to factory specs (check your service manual).
• Videos on YouTube (search "Mercruiser stuck hinge pin removal") show common techniques.

If you're working on an older R/MR drive or a specific year/model, double-check compatibility in your Mercruiser service manual, as minor variations exist.