The most common size for modern passenger cars is 14 mm, but drain plug socket sizes vary and can range from about 12 mm to 19 mm depending on the make and model.
Oil drain plugs don’t share a universal size. This article explains the typical sizes you may encounter, the different head types you might run into, and how to identify the exact size for your vehicle to avoid damage during an oil change.
Common sizes you’ll encounter
Overview of typical hex sizes
Car manufacturers use several hex sizes for drain plugs. Here’s what you’re most likely to see on passenger vehicles. This list is not exhaustive; always verify for your specific model.
- 12 mm: Found on a subset of small-engine cars and older or specialty models.
- 13 mm: Occurs on a minority of models, particularly some European/Japanese engines.
- 14 mm: The default for many modern cars, especially Japanese, Korean, and numerous American models.
- 15 mm: Appears on a few European engines and mid-size vehicles.
- 17 mm: Common on many European makes (VW/Audi, BMW, Mercedes) and various others.
- 19 mm: Less common, but used on some large engines, trucks, and SUVs.
Because drain plug head sizes vary by model and generation, don’t rely on class or price alone to determine the size. Always confirm the exact size before attempting a change.
Special head types and alternative drive styles
Non-hex and alternate drive configurations
Some drain plugs do not use a standard hex head. They may require different tools, which can impact which size you need. Here are the main non-hex variations you might encounter.
- Allen (internal hex) sockets: Some European models use a hex socket head that requires an internal Allen wrench (often 6 mm or 8 mm).
- Torx heads: A few engines use a Torx-driven drain plug (sizes vary, such as T40 or T50).
- Square or multi-point heads: Rare but possible on certain specialty or older engines.
If you encounter a non-standard head, consult the vehicle’s service manual or a parts specialist to identify the correct tool and size, rather than forcing a standard hex socket onto the plug.
How to determine the exact size for your vehicle
Steps to identify the correct socket size
To pinpoint the right size for your car’s oil drain plug, follow these practical steps. They balance speed with accuracy.
- Check the owner’s manual or service manual for the specified drain plug size and head type for your exact engine.
- Inspect the drain plug head for markings or clues about the size; some plugs have the size molded or stamped on the head.
- Measure across the flats of the hex head with a caliper or ruler to identify the closest standard size, then test the corresponding socket gently to avoid rounded corners.
- If the head is recessed or non-standard, consult the dealer or parts supplier with the vehicle’s VIN or engine type to confirm the correct tool and size.
- When reinstalling, use the torque specification from the manual and replace any sealing washers as recommended.
Accurate identification helps prevent tool damage, leaks, and stripped threads during an oil change. When in doubt, seek professional service or verify with the manufacturer’s documentation.
Conclusion and quick takeaway
There is no universal drain plug size. While 14 mm covers a large portion of modern vehicles, many cars use 17 mm or other sizes depending on the maker and engine. Always verify the exact size before loosening the plug to avoid damaging the head or threads.
Summary
In practice, expect a 14 mm hex for many contemporary cars, but be prepared for 17 mm or other sizes based on the vehicle. Confirm the correct size from the manual, the plug itself, or a reputable parts source before performing an oil change to ensure a clean removal and proper reinstallation.