Grey Variable Tension Hand Finger Exerciser Grip Trainer for Ukulele/Guitar/Bass/Piano/Saxophone/Violin/String/Wind Instrument World First 5 pressing keys to practice finger-interval. Precise design for spring structure with copper nut and screw, and the product has a lifetime warranty. Visable physical force adjustment, you can see the change while you practise. Perfect tool for pre-show warm-ups and maintaining conditioning when away from your instrumen Widely used for finger exercise when you play guitar,piano or orchestral instruments.