As the original owner of my 95 Jimmy 4.3w motor, I have found that my oil drain plug is leaking slightly and want to replace it. Most web sites give me 2 sizes for this motor....M12-1.75 or 1/2"-20. does any one know for sure? I want to get a single oversize one and repair it.
Any other suggestions appreciated.

Thanks in advance

Auto Zone shows 1/2-20 rule of thumb is if it has a 9/16 head it is 1/2 if it has a 15 mm head and or oil pan is aluminum it is M12-1.75

1995 and older use 1/2x20 and 1996 and newer use M12x1.75

Thanks for the replies...as per your info it appears to be 1/2x20.
Much appreciated!

When looking at the bolt a US size will have hash marks usually 3 or 6 and a metric bolt will have a number located on the head.