What size is the transmission fill plug?

There is no universal size for a transmission fill plug—the exact size depends on your vehicle’s make, model, year, and the specific transmission code. To confirm the correct plug size, consult the official service manual or parts catalog for your car, or share your vehicle details so I can help identify the exact plug and tool you’ll need.

Why plug size varies across vehicles

Transmission fill plugs come in different head designs (hex, Allen, or square) and different thread sizes. Manufacturers specify a fill plug size to suit fluid capacity, sealing method, and space constraints. Using the wrong size can damage the plug or strip threads and may lead to leaks or improper filling. Because there’s no single standard, always verify against your specific vehicle specifications.

How to determine the exact size for your vehicle

Use these steps to identify the correct fill plug size for your car without guessing. This reduces risk and helps you prepare the right tool and replacement parts if needed.

Use these steps to identify the exact fill plug size for your vehicle:

1. Locate the fill plug on the transmission case (usually on the side of the housing) and note the head type (socket/Allen/square) and approximate size by sight.


2. Look for any size markings stamped on the plug head or on the surrounding area of the transmission; some plugs have a size or part code printed or engraved.


3. Refer to the official owner's manual or the factory service manual for your exact year, make, model, and transmission code to confirm the plug size and the required torque specification.


4. If manuals aren’t readily available, measure the plug head with a caliper or ruler and use a thread pitch gauge to identify the thread pitch; you can also compare the plug to known reference plugs at an auto parts store.


5. Cross-check with a reputable parts catalog or dealer to confirm the plug size, thread type, and replacement part numbers before purchasing or installing.


6. When in doubt, consider a professional inspection to avoid cross-threading, leaks, or contamination during a fluid service.

By following these steps, you can identify the exact fill plug size for your vehicle and avoid common mistakes during a transmission service.

Common patterns and practical notes

While not universal, some broad patterns help you prepare:

• Many manual transmissions use metric head sizes in the low-teens for the fill plug (head across flats often around 12–14 mm), but variations exist between brands and models.


• Some transmissions use non-standard head types, such as recessed Allen keys or square-drive plugs, which require specific tools.


• Automatic transmissions with dipsticks or sealed ports may have different service plugs or no traditional fill plug; always verify for your specific unit.

If you still can’t locate the exact size, a dealership or qualified mechanic can confirm the precise plug size and torque specification for your vehicle. Providing your VIN or the transmission code can speed up this lookup.

Practical steps if you’re preparing for a fill or drain service

Before you attempt a fill or drain, keep these tips in mind to minimize risk and mess.

• Use the correct tool for the plug head to avoid rounding or stripping.


• Have a drain pan and rags ready; ensure the vehicle is level and the transmission is at the correct temperature if your procedure requires it.


• Use the recommended transmission fluid type and fill level procedure as specified by the manufacturer.


• Inspect the plug and threads for wear; replace the plug if it shows damage or cross-threading signs.

Following these steps reduces the chance of leaks or damage and ensures a proper fill during service.

Ask for vehicle-specific help

To get an exact plug size quickly, provide your vehicle’s year, make, model, engine, and whether the transmission is manual or automatic. If you have the transmission code or VIN, I can help pinpoint the exact plug size and the corresponding torque, or guide you to the exact service manual page.

Summary

The transmission fill plug size is not universal and must be looked up for each vehicle. Start with the official service manual or parts catalog for your exact model, identify the plug head type and thread, and verify via measurement or a reputable parts source. If you share your vehicle details, I can help determine the precise size and tool needed, ensuring a correct and safe service.

What size is the transmission drain plug?

There is no single size for a transmission drain plug; the size varies significantly depending on the vehicle's make and model, with common sizes including M12-1.75, M14-1.50, and 15/16 inch. To find the correct size, you must check your vehicle's owner's manual, look up the part number for your specific car, or visually inspect the plug and match it to the correct socket size.
 
You can watch this video to learn how to remove the transmission drain plug of your vehicle: 43sHow To Escape: DIY, Tips, and ReviewsYouTube · Oct 8, 2020

• Common sizes: Some common drain plug sizes include M12-1.75, M14-1.50, and 15/16 inch, O'Reilly Auto Parts, Dorman Products, Amazon.com, and Amazon.com. 
• Metric vs. SAE: Many modern vehicles use metric sizes like M14-1.50, while older vehicles may use standard (SAE) sizes like 15/16 inch, Amazon.com and K Series Parts. 
• Other common sizes: Other less common but still used sizes include M10-1.50, M18-1.50, and others, Amazon.com and Amazon.com. 
• How to be sure: The most reliable way to know is to check the owner's manual, look for the part number, or go to an auto parts store that can look up the correct size for your specific car. 

What size socket do I need for my oil plug?

The correct socket size for an oil plug depends on your car's make and model, as there is no single universal size. Common metric sizes include 14mm, 15mm, 17mm, and 19mm, while some older vehicles may use SAE sizes like 3/8" or 1/2". Always inspect the plug to confirm the size, as using the wrong socket can damage the bolt head. 
You can watch this video to learn how to change the oil in a Honda CR-V, including removing the drain plug: 1m1A Auto: Repair Tips & Secrets Only Mechanics KnowYouTube · Aug 13, 2018
How to find the right size

• Check your owner's manual: This is the most reliable way to find the correct size for your specific vehicle. 
• Inspect the plug: Visually examine the drain plug to determine its size. You can also measure it with a caliper if needed. 
• Try common sizes: If you can't find your manual, start with common metric sizes like 14mm, 15mm, 17mm, or 19mm. 
• Use the right socket type: A 6-point socket is recommended over a 12-point socket to prevent stripping the bolt head. 

This video demonstrates how to use a drain plug removal tool with a magnetic feature: 52sScavenger1320YouTube · Feb 23, 2024
Important tips

• Use the correct socket: A well-fitting socket is crucial to avoid rounding the bolt head. 
• Tighten properly: Do not overtighten the drain plug, as this can strip the threads. Tighten it to the manufacturer's specifications, or just snug it up if you don't have a torque wrench. 
• Replace the crush washer: It is a good practice to replace the crush washer on the drain plug to ensure a proper seal. 

Why does my transmission fill plug keep popping out?

Likely your transmission vent hole is clogged and the transmission fill plug popped out from the pressure buildup. Go check your transmission vent hole and if clogged, clean out the gunk.

What size is the transmission plug washer on a Honda?

18mm
Honda Genuine OEM Automatic Transmission Drain Plug Washers (18mm), Bag of 5-90471-PX4-000.