Where can I find the proper diameter copper washers for the oil pan plug? I ordered some spare ones a year ago and they are too small. They are not anymore listed in the Motorsport catalog and I think they came from them

In the meantime, I use teflon tape and works fine.

What is the ID 11/16?

Nissan still stock them. Part no. 11026-61000. As I recall, they're under two bucks.

any auto parts store should stock the plug and the washer. When I stripped mine out, I believe it was less than $5.

When I bought my car, the PO had used a thick fiber (paper) washer and RTV on mine. I bought a coper washer at a local parts house, it was something like 50 cents. Take the plug with you to match it up, if you can.

Stock plug is about .640 inch diameter at thread OD. A 16 mm gasket provides a good fit if you can get it past the threads on the plug.