What Size Bolt Is a Drain Plug?

There isn’t one universal drain plug size. For automotive engine oil pans, the most common thread sizes are metric M14×1.5, M12×1.25, M15×1.5, and M16×1.5; in older North American vehicles you may also see SAE sizes such as 1/2″-20, 5/8″-18, or 3/4″-16. Wrench heads frequently range from 13–19 mm (or 3/8″–3/4″), and some plugs use internal hex (Allen) or Torx. The exact size varies by make, model, and application, so the reliable way to know is to check the owner’s manual, a parts lookup by VIN, or measure the existing plug’s diameter and pitch.

Why Drain Plug Sizes Vary

Automakers and equipment manufacturers choose drain plug sizes based on oil pan material, available space, sealing method, serviceability, and regional standards. Metric threads dominate modern passenger vehicles, but older or heavy-duty North American applications may use SAE threads, and certain transmissions, transfer cases, and small engines use tapered pipe threads (NPT). Even within a brand, different engines and model years can use different plug sizes, pitches, and sealing washers.

Common Drain Plug Sizes and Types

The following list summarizes sizes you’re most likely to encounter on passenger vehicles and light trucks, plus notes on other driveline components. Use it as a guide; always verify specifics for your vehicle.

• Engine oil drain plugs (metric, most common today):
  – M14×1.5 (very common across Toyota, Honda/Acura, Hyundai/Kia, Ford/GM modern metric, VW/Audi, Mercedes)
  – M12×1.25 (common on Nissan/Infiniti and some older Toyota/Honda applications)
  – M15×1.5 (seen on some BMW/Mini and European models)
  – M16×1.5 (common on Subaru and some European engines)
• Engine oil drain plugs (SAE, more common on older U.S. vehicles and some trucks):
  – 1/2″-20, 5/8″-18, 3/4″-16 (varies by engine/pan)
• Other plugs (transmissions, differentials, transfer cases):
  – Metric straight threads such as M18×1.5, M22×1.5, often with crush washers
  – Tapered pipe threads like 3/8″ NPT or 1/2″ NPT on some transfer cases and small engines
  – Internal hex sizes (e.g., 8 mm, 10 mm) or Torx on some European units
• Typical wrench head or drive styles:
  – External hex heads: 13 mm, 14 mm, 15 mm, 17 mm, 19 mm (or 1/2″, 9/16″, 5/8″, 3/4″)
  – Internal hex (Allen): commonly 6–10 mm
  – Torx or specialty heads on certain European vehicles

These are the most frequently encountered patterns, but they are not exhaustive. A quick parts lookup by VIN or measuring your existing plug ensures a precise match.

How to Identify Your Drain Plug Size

If you don’t have the size on hand, these steps will help you determine it accurately without risking damage to the oil pan.

1. Check documentation: Look in the owner’s manual or factory service manual. Many list thread size, gasket type, and torque.
2. Run a VIN-based parts lookup: Dealer catalogs and reputable online parts sites will surface the exact plug and washer.
3. Measure the old plug: Use a caliper to measure the thread’s outside diameter (e.g., approx. 14 mm for M14; approx. 0.50″ for 1/2″).
4. Determine thread pitch: Use a thread pitch gauge. Common pitches are 1.5 mm for M14, 1.25 mm for M12. For SAE, count threads per inch (TPI), e.g., 20 TPI for 1/2″-20.
5. Identify thread type: Straight threads (metric/SAE) seal with a crush washer or O-ring; tapered threads (NPT) seal on the threads and should not use a crush washer.
6. Match the sealing washer: Choose the correct inner diameter (ID) and material (aluminum, copper, or fiber) specified for your plug.
7. Verify torque specifications: Install to the manufacturer’s torque spec to avoid stripping aluminum pans or under-tightening.

Following these steps reduces the risk of cross-threading or leaks and ensures you buy the right plug and washer the first time.

Washers and Torque: Don’t Overlook the Details

Most straight-thread drain plugs seal with a crush washer (aluminum or copper) or a bonded sealing washer. Replace the washer at each oil change. Typical torque ranges for engine oil drain plugs are approximately:
– M12: 18–25 lb-ft (25–34 N·m)
– M14: 25–33 lb-ft (34–45 N·m)
– M16: 30–40 lb-ft (41–54 N·m)
Always use the factory torque spec for your engine and pan material; aluminum pans often require the lower end of the range. Over-tightening can strip threads or crack the pan, while under-tightening can cause leaks.

Special Cases Beyond Engine Oil

Not all “drain plugs” are engine oil drains. Motorcycles frequently use M12×1.5 or M14×1.5 with aluminum crush washers. Many small engines (mowers, generators) drain through pipe-thread plugs such as 3/8″ NPT. Differentials and manual transmissions may use larger metric plugs (e.g., M18×1.5, M22×1.5) with internal hex drives, or tapered pipe threads. Always verify the thread type before applying sealants or washers.

Illustrative Examples by Make (Always Verify)

The following examples are common starting points reported across service literature and parts catalogs. Because engines and years vary, confirm by VIN or service manual.

• Toyota/Lexus: Often M14×1.5 on modern models; older engines may use M12×1.25. Uses aluminum crush washers.
• Honda/Acura: Commonly M14×1.5 with a 17 mm head; some older models used M12×1.5. Aluminum crush washer recommended each change.
• Nissan/Infiniti: Frequently M12×1.25 for many engines; verify pitch by model/year.
• Subaru: Commonly M16×1.5 with an aluminum crush washer.
• BMW/Mini: Often M12×1.5 or M14×1.5; some late models use specialty or composite plugs with O-rings—replace per spec.
• VW/Audi: Commonly M14×1.5; internal hex heads are typical on some engines and gearboxes.
• Mercedes-Benz: Frequently M14×1.5 with copper or aluminum sealing washers; torque varies by engine family.
• Ford: Mix of SAE on older vehicles and M14×1.5 on newer; popular truck engines often use M14×1.5.
• GM/Chevrolet/GMC: Commonly M14×1.5 on many modern engines; some applications use M12×1.75. Verify by engine RPO.
• Hyundai/Kia/Mazda: Frequently M14×1.5 on late-model vehicles.

Use these as guidelines only. The correct part number and torque spec for your exact engine is the authoritative source.

If the Drain Plug or Pan Is Damaged

Stripped threads or persistent leaks require quick attention. These are common solutions used by professionals and DIYers.

• Replace the plug and sealing washer with the correct size and material.
• Use an oversize/self-tapping repair plug as a temporary fix when threads are lightly damaged.
• Install a thread repair insert (Heli-Coil or Time-Sert) for a durable, correct-size repair.
• Replace the oil pan if damage is severe or repeated repairs have failed.
• Consider a drain valve (e.g., Fumoto/EZ drain) to reduce future wear on pan threads.

Choose the repair based on the pan material, damage extent, and long-term plans for the vehicle. A proper thread insert often restores full strength.

Summary

There is no single “drain plug bolt size.” The most common automotive engine oil sizes are metric M14×1.5, M12×1.25, M15×1.5, and M16×1.5, with older SAE sizes still seen on some U.S. vehicles. Confirm your exact size via the manual or a VIN-based parts lookup, match the correct sealing washer, and tighten to the specified torque to avoid leaks or damage.

What size bolt is the oil drain plug?

What size wrench to use for an oil drain plug depends on the size of the oil drain plug itself, which is a long bolt head. There is no universal oil plug size, but they do come in just a few several standard sizes, such as ¼ inch (. 6 centimeters), 3/8 inch (. 9 centimeters), ½ inch (1.3 centimeters), etc.

What size is a drain plug?

Oil Drain Plug Standard M12-1.5, Head Size 17Mm.

Are all oil drain bolts the same?

Different oil drain plugs and Gaskets are required for different vehicles. Drain plugs & gaskets vary from make, model, and even year. We recommend always checking your owners manual or any parts lookup like our Application Search to find the right drain plug.

What size socket do I need to remove a drain plug?

As others have said, a 12 or 8 point (divisible by 4) will work to get in there. If a specific wrench size fits, it requires a larger sized socket to fit said fastener. It might require a 1/2”-11/16” socket to fit over the flats and bite on the corners of the plug.