Control track record/playback head.
An electromagnetic head (fig 1-18) is
b. A difference may be noted in the depth, width, and length of the control
track head as compared to the normal audio head due to reduced fidelity
requirements; i.e., .020 mils for a control track head as compared to .040 to .045
for a standard audio head.
Control track record playback head showing width, depth and length