[sdiy] Appropriate knob size for Fracrack modules?

[Jonathan Lutz]

OK -- I sort of like these PKES-series knobs as shown here:
http://www.newark.com/product-details/text/CD121/5250.html

However they come in a variety of sizes/diameters (.748", .855",
1.012", 1.296").  Since I have no finished modules as reference, could
anyone tell me what the best size to order would be for Fracrack-sized
modules?

Thanks!
JON