Femitu Roller String Trees String Tree Guide Retainer Black High Quality Guitar Parts 2PCS package included: 1 pair guitar string trees black One pair of double roller string trees with mounting screws.Special rolling design improves performance of even the best set-up guitars. Improves performance for your guitars,it stress on your strings which allows the guitar to stay in tune longer Base is 6mm wide x 11.5mm length Roller width is 10mm;Roller diameter is 5mm; String Spread(center to center) is 7 mm