The Barrel knob was used by Fender on the "No-caster," Broadcaster® and Telecaster® from 1954, and also on many lap steel guitars from the '40s and '50s.
Many players including Danny Gatton prefer the low profile of this black plastic knob.
The barrel knob for CRL switches fits a .052" x .188" (1.32mm x 4.78mm) lever stem.
The barrel knob for metric switches fits a .047" x .138" (1.2mm x 3.5mm) lever stem.
Important! Measure your switch lever stem before you order a replacement knob.