From Gruv Gear:

Finally, a professional string dampener / muting accessory that every studio, session player, and tapping aficionado should have! Slide on a FretWrap to effectively cut overtones and sympathetic resonance during recording, live performance, two-hand tapping, or any creative situation where you need that extra muting hand for cleaner takes without the unwanted string noise or ringing.

The adjustable strap lets you fine-tune the pressure and dampening of the strings. Quickly slides over the headstock when not in use. No special guitar modification, installation, or tools required - Yet amazingly effective!

• SM - Fits 4-string basses, 6-string electric and acoustic guitars, and ukeleles
• MD - Fits 5-string basses & 6-string classical guitars
• LG - Fits 6-string basses & 7- to 8-string guitars
• XL - Fits 7- to 12-string basses, Chapman Sticks, double basses & other extended range guitars