Usually, to hold the barb in place O-rings are used.

Massimo Quattrone, Product Manager in Salvimar, suggests to use shorter shafts, which in his opinion do not determine loss of the line of aim, but permit a simple blocking of the barb when positioned on top of the shaft, simply passing the line in the traditional way and over the barb itself. A nice simplification! In the photo the process done on the New Salvimar Metal.