Done a search, can't seem to find the answer.

What is the thread size, in mms please, of the oil sump plug on a 1997 SOHC 4.0 litre engine?

My current sump plug is good, but i am not sure what size of o-ring to use in the hole around it, so i am thinking i will just buy a new one with a copper washer, as i know somewhere that sells them.

You can pick up a new plug from any Ford dealership for about $10, and it includes a new washer for it. As far as I know, the rubber washer is available separately for a couple of dollars as well.

Replacing that o-ring with a regular rubber o-ring or a copper washer will not work well for long. It will leak, drip, loosen up, or all three. You need the right part for the job.

Contact Torrie at www.fastpartsnetwork.com

-Joe