[Hallicrafters] SX-71 Bandspread/MainTuning Knobs Question

[Julian Bunn]

I am puzzled why none of the three SX-71s in my possession have metal 
ring inserts in the
Bandspread and Main Tuning knobs, whereas the Hallicrafters manuals and 
Sams Photofact
folders for the SX-71 show the knobs complete with metal rings attached 
to the inside perimeter
of each knob.

Were these metal rings poorly attached, and did they eventually fall out 
and get lost?
Or were the knobs with metal rings only attached to Run 1 units? (I have 
seen a
recent picture of a white face SX-71 that has the ring inserts.) What 
are the
metal rings made of, and how easy would it be to make a replacement ring?

On a related topic: If anyone has SX-71 CW Pitch, Tone, Volume and 
Sensitivity
knobs for sale, please let me know, as I am looking for all four.

Best wishes,
Julian