What Size Is an Oil Bolt?

There isn’t one universal “oil bolt” size. For most passenger cars, the engine oil drain bolt is commonly M14×1.5, but many engines use M12×1.5, M12×1.75, M16×1.5, or even SAE threads like 1/2″-20. If you mean an oil-line banjo bolt, sizes often include M10×1.0 or M12×1.25. The exact size depends on the vehicle and application, so check your service manual or measure the existing bolt. Below is a detailed guide to help you identify and confirm the right size.

What “oil bolt” usually refers to

Most people use “oil bolt” to mean the engine oil pan drain plug. However, the term can also refer to bolts in the lubrication system such as banjo bolts that feed oil to turbos or cylinder heads. Each has different thread sizes, head sizes, and sealing methods.

Common sizes by application

The following list summarizes frequently encountered sizes for engine oil drain plugs, motorcycle drain bolts, small engines, and oil-line banjo bolts. These are examples, not guarantees—always verify for your specific model.

• Passenger cars/light trucks (engine oil drain bolts):
  

  • Metric: M14×1.5 (very common), M12×1.5, M12×1.75, M16×1.5, occasionally M20×1.5
  • SAE: 1/2″-20 UNF (older American engines), less commonly 3/4″-16 on certain applications
  • Typical hex head: 13–19 mm; sealing via aluminum/copper crush washer or integrated gasket

• Motorcycles:
  

  • Common: M12×1.5, M12×1.25, M14×1.5 (varies by manufacturer)
  • Hex heads often 12–17 mm; crush washer required

• Small engines (mowers, generators, power equipment):
  

  • Common: M12×1.5, 1/2″-20 UNF; some use drain valves instead of bolts

• Oil-line banjo bolts (turbo feeds, oil galleries):
  

  • Common: M10×1.0 (fine), M12×1.25, M12×1.5; specialized to the component
  • Use copper crush washers on both sides of the banjo fitting

These patterns reflect what parts counters and service departments see most often, but manufacturers can and do specify different sizes by engine family and year.

How to identify your oil bolt size

If you don’t have the spec on hand, you can measure and confirm the size with basic tools. The steps below help you determine thread diameter, pitch, and sealing type.

1. Remove and clean the bolt: Wipe threads to remove oil and debris.
2. Measure major diameter: Use calipers across the outer thread peaks.
   

   • ≈14.0 mm indicates M14; ≈12.0 mm indicates M12; ≈12.7 mm indicates 1/2″ SAE

3. Determine thread pitch:
   

   • Metric: Use a pitch gauge (1.5, 1.25, 1.75 mm common)
   • SAE: Count threads per inch (20 TPI common for 1/2″)

4. Check the sealing method: Look for a separate crush washer (flat, soft metal) or an integrated gasket on the bolt.
5. Inspect the pan/threaded hole: Ensure threads are straight (not tapered). Engine oil pans are almost always straight-thread, not pipe-thread.

Confirming these details prevents cross-threading and leaks, and ensures you buy the correct replacement bolt and washer.

Crush washer and gasket sizing

Even when the bolt threads are correct, an incorrect washer can cause leaks. Here’s how washer sizing typically maps to bolt size.

• Match the washer’s inner diameter (ID) to the bolt size:
  

  • M12 bolt → 12 mm ID washer; M14 bolt → 14 mm ID; M16 bolt → 16 mm ID

• Common materials: aluminum or copper (single-use recommended); some OE washers are bonded rubber/metal and can be reusable if specified.
• Typical thickness: ~1.5–2.0 mm; outside diameter varies by application (e.g., M14 washers often ~20–24 mm OD).

Using the correct washer type and size is as important as the thread match; it ensures proper sealing at the specified torque.

Torque guidance (check your manual)

Torque specs vary by manufacturer, bolt size, washer material, and oil pan material (steel vs. aluminum). The ranges below are common, but always verify the exact spec for your vehicle.

• M12 drain bolt (many motorcycles/some cars): about 20–30 N·m (15–22 lb·ft)
• M14 drain bolt (many cars): about 30–45 N·m (22–33 lb·ft)
• M16 drain bolt (some larger engines): about 35–55 N·m (26–41 lb·ft)
• Banjo bolts: highly application-specific; follow component/service manual exactly

Always install a fresh crush washer unless the manual specifies reusability, start threads by hand to avoid cross-threading, and use a torque wrench to prevent stripping—especially in aluminum pans.

Where to find the exact specification

If you need a definitive answer for your vehicle, these sources provide the correct size and torque.

• Owner’s manual or factory service manual: Lists drain plug size, washer type, and torque.
• OEM parts catalogs (online dealer sites): Look up by year/make/model; note the part number and size.
• Aftermarket parts databases: Cross-reference drain plug kits (e.g., by Dorman, OEM suppliers) for size and washer.
• Label on the oil pan plug (some aftermarket magnetic plugs print the size).
• Local dealer or parts counter: Provide VIN for precise fitment.

Documenting the OEM part number makes future purchases simpler and reduces the risk of leaks or damage from mismatched threads.

Summary

There is no single oil bolt size. For engine oil drain plugs, M14×1.5 is very common, but M12×1.5, M12×1.75, M16×1.5, and SAE sizes like 1/2″-20 are also widely used; oil-line banjo bolts often run M10×1.0 or M12×1.25. Verify your exact size through the manual or measurement, match the correct crush washer, and tighten to the specified torque to ensure a proper seal without damaging threads.

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 tool should you use to loosen the oil pan drain plug?

Play. So let’s go ahead open it up really quick. Yeah we’re going to use some tin snips why. Not cuts right through. There. And there we go just a little flexible dongle deal thingy.

What size is the oil plug bolt?

There isn’t a universal oil plug bolt size; the size varies by vehicle make and model, but most common sizes are in the M14 to M19 range for metric bolts. To find the correct size, check your owner’s manual or use digital calipers to measure the bolt’s thread diameter to find the correct thread pitch (e.g., M12 x 1.5). 
To determine your oil plug bolt size:

1. Consult Your Owner’s Manual: This is the most reliable way to find the exact size for your specific vehicle. 
2. Measure the Bolt:
   • Use a ruler or digital calipers to measure the diameter of the bolt’s threads. 
   • This measurement will give you the first part of the bolt size (e.g., if it measures 12mm, the bolt is likely an “M12”). 
3. Look for Common Thread Pitches: After identifying the diameter, find the corresponding thread pitch (the distance between the threads), which is usually listed as the second number in the bolt size designation (e.g., M12 x 1.5). 
4. Identify the Wrench/Socket Size: The wrench or socket size needed to remove the plug is the same as the bolt head size, which is often 14mm or 15mm for common metric plugs. 

What size socket do you need for an oil pan?

There is no universal oil pan socket size; the specific size depends on the vehicle’s year, make, and model, but common sizes include 15mm, 16mm, or 9/16-inch. To find the correct socket, you’ll need to check your vehicle’s manual or visually inspect the drain plug itself, as a proper fit is crucial to avoid rounding the bolt head. 
How to find the right socket size:

1. Check your vehicle’s manual: or a reliable parts website for your specific car. 
2. Visually inspect the drain plug: before you start your oil change. The size of the wrench needed corresponds to the width across the bolt’s flats. 
3. Have a basic metric socket set: on hand, as common sizes range from 10mm to 21mm, with 15mm being a frequent choice. 

Tips for success:

• Use the correct size: A socket that is too small can damage the bolt head, while one that is too large can also cause issues and damage. 
• Use a 6-point socket: This type provides a more secure fit on the bolt head, reducing the risk of stripping. 
• Clean the bolt and pan: Ensure the bolt and surrounding area are clean before reinstalling to maintain a proper seal and prevent future leaks. 
• Consider writing it down: For future reference, note the drain plug size under the hood of your car.