What size socket is a drain plug?
There isn’t a universal drain-plug socket size. For oil drain plugs, 14 mm hex is the most common on modern cars, though some models use 12 mm or 17 mm. Transmission and differential drains vary more widely and may use hex, Allen, or Torx heads. Always check the vehicle’s manual or measure the plug head to confirm the correct size.
Common drain plug sizes by application
Below is a general guide to the sizes you’re most likely to encounter. Exact sizes depend on the make, model, and year.
- Oil pan drain plugs: The vast majority use a 14 mm hex head; alternatives you may see include 12 mm or 17 mm on certain makes.
- Transmission drain plugs: Common heads include 14 mm or 17 mm hex, but some transmissions use an 8 mm Allen key, Torx, or other head types. Verify for your specific transmission.
- Differential drain plugs: Often 14 mm or 17 mm hex, with some applications using other sizes or head types. Check your axle’s service information.
- Radiator drain plugs/petcocks: Many are plastic or use a small screw-type petcock rather than a standard hex plug; if a metal drain plug is present, it’s typically in the 8–10 mm range or uses a different head style.
Because head shapes and sizes vary, consult the vehicle manual or measure the plug to avoid damage from using the wrong socket.
How to determine the exact size for your vehicle
Use a methodical approach to confirm the correct socket size for your drain plug on your specific vehicle.
- Identify the drain plug and its head type (hex, Allen, Torx, etc.).
- Consult the owner’s or service manual for the recommended size and torque specification.
- Test-fit sockets starting with the most common sizes (for oil, 14 mm; for others, try 12, 14, 17 mm; and consider Allen or Torx if indicated).
- Do not force a size that doesn’t fit; if the head is damaged or no size fits, replace the plug or seek professional help.
Having the right socket size helps prevent stripped heads and leaks during service.
Head types you’ll encounter
Drain plugs come in hex, Allen, Torx, and sometimes square-drive or unusual configurations. Knowing the head type is as important as knowing the size, because a plug might be 14 mm across flats but require an Allen key head rather than a hex socket.
Summary
There’s no single socket size for all drain plugs. Oil drain plugs are most often 14 mm, with 12 mm and 17 mm as common alternatives. Transmission and differential plugs vary more widely and can use hex, Allen, Torx, or other head types. Always verify with the manual or by measuring the plug head, and carry a small set of sockets to ensure you use the correct size to avoid damage.
