What mm is an oil plug? Understanding sizes, tools, and how to find the right one

There isn’t a single standard size for oil drain plugs: most passenger vehicles use metric threads in the M12–M14 range (commonly M12×1.25, M12×1.5, M14×1.25, or M14×1.5) with hex heads typically 13–17 mm, while some trucks and performance or diesel engines step up to M16–M18 or larger. To be certain, check your specific vehicle’s service data or measure the plug you have.

Why there’s no single “mm” answer

“Oil plug” usually refers to the engine oil drain plug. Manufacturers choose different thread diameters and pitches based on engine and oil pan design, and they may also specify different head styles (external hex, internal hex/Allen, or Torx). Two dimensions matter: the thread (for sealing and fit) and the head or bit size (the tool you use). These are not the same number, which is why you might need, for example, a 17 mm socket for a plug that has M14×1.5 threads.

Common oil drain plug thread sizes

The following are widely encountered thread sizes on modern vehicles. Use this as a reference point, not a substitute for your vehicle’s official specification.

• M12×1.25 or M12×1.5 – Common on many small to midsize engines and motorcycles.
• M14×1.25 or M14×1.5 – Very common across many Japanese, European, and American passenger vehicles.
• M16×1.5 – Found on some larger-displacement engines and light trucks.
• M18×1.5 – Seen on some trucks, diesels, and high-capacity sumps.
• Less common/legacy: UNF or NPT threads on older domestic vehicles and certain aftermarket pans; verify carefully before ordering.

Crush washers and sealing rings are sized to the thread diameter (e.g., a plug with M14 threads typically uses a washer sized for 14 mm ID). Always match the washer to the thread size and material the manufacturer specifies.

Typical socket and bit sizes used on drain plugs

Even with the same thread size, the head type can vary. Below are tool sizes you’re likely to encounter when removing an oil drain plug.

• External hex sockets: 13 mm, 14 mm, 15 mm, 17 mm, and 19 mm are most common; some trucks use 22–24 mm.
• Internal hex (Allen): 6 mm or 8 mm on some European applications.
• Torx/Star: T45 or T50 on certain modern designs and plastic drain plugs.
• Specialty: Magnetic or valve-style replacement plugs may include their own tool interface; follow the maker’s instructions.

Remember that the socket/bit size refers to the head you turn, not the thread size. Using a poorly fitting tool risks rounding the head or damaging the pan.

How to find your vehicle’s exact plug size

If you don’t already know your size, follow these steps to verify it confidently and avoid leaks or damage.

1. Check the owner’s manual or factory service manual for the drain plug specification (thread, pitch, and torque).
2. Look up the OEM part number by VIN on the manufacturer’s online parts catalog; cross-reference the listed thread size and washer.
3. Measure your existing plug with a caliper and a thread pitch gauge once it’s removed (never force a “close” size).
4. Bring the plug to a reputable parts store; they can match thread and washer sizes and confirm the correct replacement.
5. Always replace the crush washer or sealing ring and torque the plug to the OEM spec; overtightening can strip aluminum pans.

Avoid guessing between similar sizes (e.g., M14×1.25 vs. M14×1.5). A mismatch can cross-thread the pan, leading to costly repairs.

What different brands often use (indicative, not exhaustive)

The patterns below are common, but there are many exceptions. Always verify for your exact model, engine, and year.

• Japanese brands (Toyota, Honda, Nissan, Mazda): Frequently M14×1.5 or M12×1.25; head sizes often 14–17 mm.
• European brands (VW/Audi, BMW, Mercedes-Benz): Often M14×1.5; some use internal hex or Torx heads, and certain modern VAG pans use plastic drain plugs.
• American brands (Ford, GM, Ram): Commonly M14×1.5 or M12 variants on cars; larger trucks may use M16–M18 with larger hex heads.
• Motorcycles: Commonly M12×1.5 or M14×1.5 with a 17 mm external hex head, but check your model.

Because running changes happen within the same model line, the safest route is still the official spec for your exact VIN.

Torque and washer guidance

Proper sealing depends on the correct washer and torque, not just thread size. Keep these general practices in mind.

• Typical torque ranges: roughly 20–40 N·m (15–30 ft·lb) for many passenger cars, depending on thread size and pan material. Always use the manufacturer’s spec.
• Use the correct washer type and size: copper, aluminum, steel with gasket, or composite as specified. Replace at each oil change unless the maker explicitly says it’s reusable.
• Clean mating surfaces and inspect threads; if you see galling or aluminum swarf, stop and assess before reinstalling.
• Do not use thread sealant or PTFE tape on plugs designed to seal with a washer; it can affect torque and sealing.

Following the OEM torque and washer spec is the best protection against leaks, stripped threads, and pan damage.

Quick clarifications

These common questions help avoid mix-ups between thread and tool sizes.

• Is a 14 mm socket the same as an M14 plug? No. The socket size is the head you turn; M14 refers to the plug’s thread diameter.
• Can I substitute a close thread pitch (e.g., M14×1.25 instead of M14×1.5)? No. A pitch mismatch will cross-thread and can ruin the pan.
• Can I reuse the crush washer? Generally not recommended; many are single-use and reusing can cause seepage.
• Are magnetic plugs worth it? They can help capture ferrous particles but do not replace regular oil/filter changes or diagnostics.

When in doubt, verify specifications rather than forcing parts that “almost” fit.

Summary

There is no universal millimeter size for oil drain plugs. Most passenger vehicles use M12–M14 metric threads with 13–17 mm heads, while some trucks and larger engines use M16–M18 or more. The only reliable answer for your vehicle is its exact specification: confirm via the manual or OEM parts catalog, or measure the plug and pitch precisely. Always use the correct crush washer and torque to the manufacturer’s spec to ensure a leak-free, damage-free oil change.

What socket size do I need for an oil change?

You need a socket wrench (14mm or 15mm), an oil filter wrench, an oil drain pan, a funnel, and a new oil filter.

What size is an oil plug?

There is no single standard size for an oil drain plug; the size varies by vehicle make and model. Common sizes can range from 10mm to 21mm for the wrench or socket, with common thread sizes being, for example, an M12x1.75 thread with a 15mm head. To find the correct size for your vehicle, check your owner’s manual, the product specifications, or use calipers to measure the plug’s threads yourself. 
Why there’s no universal size 

• Manufacturer Variations: Different car manufacturers use different designs for their oil pans and drain plugs, leading to variations in size.
• Component Specifics: The size isn’t universal because the oil pan, drain plug, and gasket all differ between vehicles.

How to find the correct size for your vehicle

1. Check the Manual: The most reliable way to find the correct size is to consult your vehicle’s owner’s manual or the product specifications. 
2. Measure the Plug: If you can’t find the information in the manual, you can use a ruler or digital calipers to measure the diameter of the plug’s threads to determine its size. 
3. Look for Markings: Some oil plugs have markings on their surface, such as “M12x1.5”, which can indicate the thread size. 
4. Use a Tool Kit: A socket set with a range of both SAE and metric sizes is a good investment, especially if you work on different vehicles. 

What is the size of oil drain bolt in MM?

The most common sizes for drain plugs are typically in the 14mm to 19mm range.

What size socket is a M12 oil drain plug?

M12*1.25P-H17, Hex size is 17mm, uses 17mm wrench.