Radio knob for use on shafts that have a flat side aka "D" shaft. This is also the same as part# 17513 wiper control knob.
55/56 RADIOS USE 18829S KNOBS
57 RADIOS USE (1) 18829S AND (1) 18829D KNOB
This knob is used on the wiper control and also on radio shafts' that have a "D" shaft. That is a shaft that had a flat on one side. If the radio shaft is split, then the knob to order is 18829S.