I am pretty sure it is a type "c" shoulder/sprocket/shoulder with a keyway, no set screws. Confirm this is proper for the sprocket you are looking for.

https://www.amazon.com/Azusa-Tooth-Chain-Bore-Sprocket/dp/B079Z81FMH/ref=sr_1_1?crid=142E2423YYYG4&keywords=5%2F8%22+sprocket+20t+type+c&qid=1663093168&s=industrial&sprefix=5%2F8+sprocket+20t+type+c%2Cindustrial%2C72&sr=1-1

sorry that is for a 12t.