Roller Guitar String Trees one little rollers on each tree. The rollers lessen the stress on your strings which allows the guitar to stay in tune longer. This also prevents wear and tear on the strings which results in longer string life. Base is 6mm wide x 11.5mm Total height including roller is 12mm Roller width is 10mm Roller diameter is 5mm String Spread (center to center) is 7mm Package Included: 1set Guitar String Trees