Mystery solved, at least for MY Summit 450. Saw a Utube video that showed someone doing the valves on what looked like a Summit 450, BUT, the screws looked like regular sized, and the valves looked like a black plastic body. Mine are all metal and the screw is WAY smaller. After a trip to the local hardware store, and looking through lots of bins, the winner ended up being, a 3mm size screw, metric thread, that a 2mm allen wrench fit. I went with a button head allen, lord how I hate phillips head screws. In the SAE section, I did find a 3-48 screw and a 4-40, but no 4-48.