I apologize for the sarcastic sounding reply last night. I have been around my in-laws for 4 days. What can I say? The setover screws are like Lurch says, 5/16 - 18. The drum switch knob is 1/4 - 20 on my unit. SB may have used several vendors for the switches, but 1/4 - 20 would be a real good bet.
Merry Christmas and Happy New Year