Thomastik - Spirocore Strings The sound is full and homogenous, balanced and voluminous. The string has been calibrated to satisfy the express wish of many artists for an equally effective arco and pizzicato. Spirocore's hi-tech core makes for effortless fingering, responsive bowing, stable tuning and a very long string life. With Spirocore the steel string's technical possibilities have been developed to their maximum. Dont forget to specify if you require a ball or loop if you are ordering an e string.