Happy Holiday Season, and happy shopping! The "in time for Christmas" question... I can't be certain for you, although if you are in BC or Alberta you chances are good until about the 15th. For everyone else, if you want it for Christmas please choose a tracked shipping option.
Clover makes two styles of these metal adjustable ring thimbles.
Choose the one that sits on the flat area between your knuckles or the one with the concave plate which sits at the base of your finger. Customers who sashiko stitch seem to prefer the one with the plate, which makes sense since it is used in the same way as the leather sashiko thimble. (You can find the leather sashiko thimble in the sashiko supplies on this website)