Great question — answering as the UphillTech team:
It appears that the "common feed thru" terminals are supposed to be connected together all the time inside the switch, for daisy-chaining multiple switches with jumpers between, and that in your pictured switch, the single terminal on the opposite side is the switched terminal. A Google image search on the switch picture leads to an Ebay listing for similar switches : These three pictures are from the Ebay listing. The ad identifies these, I believe mistakenly, as 4-way switches. The ad poster does not understand the common feed thru. The ad's pictured switch is a 3-way, and yours is a regular single-control (1-way?) switch. The front picture has a "P & S" stamp, which may mean Pass &...
Full answer by Triplefault: https://diy.stackexchange.com/a/333589 (CC BY-SA 4.0).
Need it done for your business? UphillTech.