The Tail Gut secures the tailpiece to the end pin (a.k.a. tail button). This much taken-for-granted accessory is more important than most musicians realise. Assuming a properly set-up instrument (i.e. bridge, sound post, etc.) of at least moderate quality with decent strings and a good bow, the adjustment of the tail gut and the material from which the tail gut is made can make a big difference to the sound.
The tailgut on this violin can be seen clearly here
Wittner tailguts are probably one of the best regarded brands on the professional circuit, but luckily they don't come in at professional prices!
See our range of tailguts and other string accessories HERE.