Tuner?

750k2

New member
I just got a tuner in trade - it is a Hoehn style and is threaded
for the regular weights but there is a secondary smaller male
threaded tube - it is stationary as you dial up and down the range.
What is it threaded for?
My other 3 do not have this.
I'm thinking some kind of bloop tube??
Thanks
 
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