Every goldsmith seems to have his own size, often as a result of his teaching or first work experience, therefore you can choose from a standard bench pin (middle) or a custom made one (left and right).
My standard bench pin fits in the benchmate system and in the mortise in my workbenches, this one is about 12cm long and 6cm wide, above you can see two examples of pins left and right, which I custom made over time, also for existing benches which weren’t made by me.
In the course of the years I have also witnessed how the bench pins found in supply stores are usually made of lesser wood species. The best species is European Beech and it is the only species I will use, Beech is hard and smooth with no visible pores and very short fibres, this makes that they last extremely long.