What size is the oil drain plug on a 350 Chevy?
The standard oil drain plug on a Chevrolet 350 small-block is 1/2-20 UNF. Some aftermarket pans or non-GM replacements may use a different size, such as 7/16-20, so always verify on your specific pan.
Standard size and what to expect
Most Chevrolet small-block 350 engines use a 1/2-inch diameter drain plug with 20 threads per inch (1/2-20 UNF). This size is common across many OEM oil pans for the 350, but variations exist depending on aftermarket components or pan design.
The following list outlines the sizes you’re most likely to encounter and why they appear on a 350 Chevy. Use this as a quick reference when shopping for a replacement plug orPan kit.
- 1/2-20 UNF: The typical size for the stock Chevrolet small-block 350 oil pan.
- 7/16-20 UNF: Occasionally used by some aftermarket pans or non-GM replacements.
- Other sizes: Rare variations may occur with custom or specialty pans; always verify by measuring the thread diameter and pitch or checking the pan’s documentation.
Conclusion on the list: When replacing the drain plug, confirm the exact size for your particular oil pan model before purchase to avoid cross-threading or leaks.
How to confirm your exact drain plug size
To ensure you buy the correct plug for your 350 Chevy, use these steps to identify the exact thread size for your oil pan plug.
- Inspect the oil pan and model year: Look up the pan part number or service manual for the recommended drain plug size.
- Measure the thread diameter and pitch: Use calipers or a thread gauge to determine the diameter and TPI (threads per inch).
- Try a test fit with a known plug: If you have a spare plug from a similar pan, thread it in gently to confirm fit without forcing.
- Check replacement part listings: When ordering a new plug, verify that the listing specifies 1/2-20 UNF for GM small-block Chevys, unless your pan states otherwise.
Note: When installing a new drain plug, avoid overtightening and replace any crush washer or gasket as required by your pan design. If in doubt, consult the service manual or a parts specialist for your specific pan model.
Summary
For a typical Chevrolet 350 small-block, the standard oil drain plug size is 1/2-20 UNF. Always verify with your oil pan’s exact model and year, as aftermarket pans can use 7/16-20 UNF or other sizes. Confirm fit before draining, replace any washers as needed, and torque according to the manufacturer’s specifications to prevent leaks and maintain proper oil sealing.
