Help! Socket Set Screw Size on Shifter

I replaced my stock shifter with an Alpha Threaded Shift Know Adapter. Somehow, someway, the set socket screw has disappeared. Anyone know the size so I can track down a replacement? I'm guessing it's around a 1.5 x 8mm? It's the lower screw that faces toward the driver side, not the higher one that faces toward the engine.

Thanks!