Cox head question

Have a small cox head that goes on a .020 or .010 but I don't know which. Diameter at the threads looks to be about .389 Can someone check and see.

Thanks

You have the (relatively) gargantuan .020. The .010 head is closer, measuring across the threads, to .250, but this is an estimate, since I didn't take my .010 head off.

Thanks!!