That it does not really fit in the MK1-3 "Fat fonts". Even the 40 with the tail appears to be a little more skinny both the #4 and the 0.
I personally don't know how to classify beyond the Mk1-3 and even in the fat fonts there are many variations which are nuances on the known versions.
I also don't think the one you presented is a service dial or the more common slim versions.
I have a few more inserts I will try to photograph and see if we can find a match.
Best
Bill