What size is the oil drain plug on a 350 Chevy engine?

On a Chevrolet 350 small-block engine, the oil drain plug typically uses 1/2-20 UNF threads. The hex head usually fits a 9/16-inch wrench, with some variations by pan design. Verify with your specific pan or service manual if you’re unsure.

This article explains the standard size you’re likely to encounter, notes common variations across production years and aftermarket pans, and provides guidance on how to confirm the exact size on your engine before maintenance or part replacement.

Standard drain plug size for the Chevy 350 small-block

The classic Chevy 350 small-block oil pan is designed for a 1/2-20 UNF drain plug. This thread size is widely used in factory pans and many aftermarket SBC pans. The plug head commonly accepts a 9/16-inch wrench, though some suppliers use a 14 mm hex. Because there can be minor differences between pan designs, it’s a good idea to check the plug you currently have or reference the pan’s specifications if you’re replacing parts.

Key specifications you should know at a glance:

• Thread size: 1/2-20 UNF


• Plug head size: commonly 9/16-inch hex (roughly 14 mm), but verify for your plug


• Sealing option: some plugs use a sealing washer or copper gasket; others seal via the plug pan interface


• Variations: aftermarket aluminum or staggered pan designs may still use 1/2-20 threads but can differ in head design or washer requirements

In summary, for a typical Chevy 350 small-block oil pan, expect 1/2-20 UNF threads with a plug head that usually takes a 9/16-inch wrench, while keeping an eye out for any pan-specific variations.

Variations and how to verify your plug size

While 1/2-20 UNF is the standard for most SBC 350 oil pans, some aftermarket pans or non-standard builds may differ. To ensure you have the correct plug size for maintenance, follow these steps:

1. Identify your engine and oil pan type (classic SBC 350 vs. other generations or aftermarket pans).


2. Inspect the current drain plug for any markings and measure the threaded portion to estimate diameter and pitch.


3. Use a thread gauge or compare with a known 1/2-20 UNF plug to verify the pitch and diameter.


4. When in doubt, take the old plug to an auto parts store to match it, or consult the GM service manual for your exact year/model.


5. Choose the correct plug with the proper thread (1/2-20 UNF) and an appropriate sealing option (washer or magnet, as required by your pan).

Following these verification steps helps you avoid leaks or cross-threading and ensures compatibility with your specific SBC 350 oil pan.

Summary

For the traditional Chevy 350 small-block engine, the standard oil drain plug uses 1/2-20 UNF threads, with a typical hex wrench size around 9/16 inch. Always verify against your particular oil pan design or service manual, as aftermarket pans and different engine variants may introduce small variations. When in doubt, bring the plug to a parts store for an exact match and replace with the correct sealing hardware.

What size socket do I need for my oil plug?

The correct socket size for an oil plug depends on your car's make and model, as there is no single universal size. Common metric sizes include 14mm, 15mm, 17mm, and 19mm, while some older vehicles may use SAE sizes like 3/8" or 1/2". Always inspect the plug to confirm the size, as using the wrong socket can damage the bolt head. 
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How to find the right size

• Check your owner's manual: This is the most reliable way to find the correct size for your specific vehicle. 
• Inspect the plug: Visually examine the drain plug to determine its size. You can also measure it with a caliper if needed. 
• Try common sizes: If you can't find your manual, start with common metric sizes like 14mm, 15mm, 17mm, or 19mm. 
• Use the right socket type: A 6-point socket is recommended over a 12-point socket to prevent stripping the bolt head. 

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Important tips

• Use the correct socket: A well-fitting socket is crucial to avoid rounding the bolt head. 
• Tighten properly: Do not overtighten the drain plug, as this can strip the threads. Tighten it to the manufacturer's specifications, or just snug it up if you don't have a torque wrench. 
• Replace the crush washer: It is a good practice to replace the crush washer on the drain plug to ensure a proper seal. 

What size socket is a Chevy Silverado oil drain plug?

I can pull it out quickly and avoid making a mess. There we go. Let's remove the oil filter it's just on the other side of the oil pan i'm going to use an oil filter. Wrench.

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

The AGS Accu-Fit® Magnetic Drain Plug Removal Tool - the ultimate solution for hassle-free oil changes. This innovative tool is a must-have for anyone who wants to avoid the risks of getting burned by hot oil while changing their oil.

What size is the oil drain plug on a Chevy 350?

The most common oil drain plug size for a Chevy 350 is M12 x 1.75 thread size with a 15mm or 3/4 inch hex head. Some older models may use a 1/2-20 thread size, so it is best to verify your specific vehicle by checking the plug or its specifications before purchasing a new one. 

• Common size: M12 x 1.75 thread, 15mm hex head 
• Alternative size: 1/2-20 thread (used in some older models) 
• Recommendation: Visually confirm the thread size and hex head size on your current plug, or consult your vehicle's service manual, to ensure you get the correct replacement.