Sold by the foot. PVC Tubing for insulating the output jack wire in a vintage style Gibson guitar. It slips over the shielded braided wire to keep it from shorting out any of the pots. 
Very similar to the vintage #8 PVC Tubing found inside vintage instruments.
 
  
 
  
 
 
 
 
  
 
  
 
  
 
  
