From D'Addario:

The D'Addario Capo Lite is made from high-strength molded ABS thermoplastic for use on acoustic, electric and classical 6-string guitars. A patented micrometer adjustment mechanism allows the player to dial in the exact tension needed for your guitar, strings, and playing position. This greatly reduces the need to retune your guitar during and after capo use. The capos molded ABS design offers lightweight, ease-of-use, and superior functionality at an affordable price. Enjoy buzz-free, in-tune performance at any fret without breaking the bank!