Thank you for visiting. We would appreciate it if you could also take a look at the comment section. When purchasing, please specify the "material and size". "Guitar String Attachment" is a part that is passed through the string to make the ball end spherical. By making it a spherical end, - Eliminates misalignment with ring-type ends and prevents string twisting! - The contact surface becomes uniform, improving the balance of string vibration! 【Types】 Brass: Outer diameter 4.0mm size set Brass: Outer diameter 4.5mm size set Aluminum: Outer diameter 4.0mm size set Aluminum: Outer diameter 4.5mm size set 【Product Contents】 4 pieces for strings 1-4 2 pieces for strings 5-6 Total 6 pieces in a set 【Differences by Type】 Brass material : Bright and lustrous tone Aluminum material : Gentle and calm tone Sustain : 4.5mm size < 4.0mm size Sound thickness : 4.0mm size < 4.5mm size *The effects vary depending on the individual guitar, so please use this as a reference. 【Compatible Strings】 Compatible with all electric guitar string gauges *Can be installed without modification. 【User Impressions】 Sustain is extended! Tuning is also stable! The harmony of the arpeggio sounds three-dimensional! The sound and vibration of the guitar have dramatically improved! The change in sound and the cost performance are amazing! I have installed them on all my guitars and can't let them go because I feel the improvement in sound! 【About Shipping】 Shipped by regular mail (3-4 days for delivery). 【Other】 The product package is for both acoustic and electric guitars. The product is the same for both acoustic and electric guitars. For electric guitars/Gibson/Ibanez/Fernandes/ESP/Fender/ Epiphone/PRS/Yamaha guitar manufacturers! An item you'll want to have along with a capo/guitar cable/tuner/effector/guitar stand/ picks/guitar amp/strap, etc.! Japan Patent Office Design Registration No. 1483662