1969 8 Track Radio knob ?

[jackrt]

Trying to restore one and it has a threaded shaft coming out on the left side at the top. i can only find one old picture on one and it shows a black knob on it. Anyone know what this was used for and does anybody make reproductions for it? thanks

 

[jackrt]

here is a shot of it.

 

[dual fours]

Trying to restore one and it has a threaded shaft coming out on the left side at the top. i can only find one old picture on one and it shows a black knob on it. Anyone know what this was used for and does anybody make reproductions for it? thanks

With an 8track in and playing, black knob would be used by pushing in to change the tracks/programs.