If your oil pan is aftermarket then unfortunately we do not have spec information for it. Although the size might be the same as the stock drain pan, this often is not the case.
When dealing with aftermarket oil pans, you will want to refer either to the parts manual or the manufacturer of the pan to find out the size of the drain bolt it uses.
If you are able to measure the plug manually, we can tell you the corresponding size. One easy way to measure your plug is to take it to a hardware store and mate it with a nut.
That size should be the one you are choosing a Fumoto valve based on.