Notions - Tulip Co. of Japan - Ring Thimble - 17.5mm - 0.68" (M-L) - is currently on backorder. You may still purchase now though and we'll ship as soon as more become available.
This thimble has tiny hexagonal holes on the surface in order to fix the eye end of the needle tightly against it. This size fits medium to large - 17.5mm (0.68") diameter. Made of nickel plated brass.