360 Transmission filter o-ring size

I just completed a major service on my 360. I changed the transmission fluid, cleaned the filter and had not ordered the o-ring seal on the filter. It is Ferrari #182199. I thought I would order a few for next time through my o-ring supplier but cannot find a size. I remember seeing it as I was browsing through information about the job and it was a strange size. Anyone have the size please?