A fishtail shank or fishtail stem refers to the pins affixed to certain models of road studs. They’re straight metal pins that separate into two thinner points towards the end of the fitting. They are an alternative to the chisel shank style of fitting.
All road studs come with a fixing that splits out into a cross shape, the primary reason for this is to prevent churning or turning in place once installed. The usage they’ll undergo from both vehicle traffic and pedestrian traffic alike will put a lot of strain on the pin underneath, and they are designed so that this pressure won’t unseat or shift them. Fishtail shanks provide extra resistance, over and above the initial design, to combat turning post-installation.
Fishtail shanks are available on both aluminium and stainless steel road studs.