A capo is structured and configured to permit rapid installation and tightening thereof on a stringed instrument. The capo includes a yoke with a central support member, a string-contacting clamping bar which is pivotally attached to the yoke, and a spring-loaded release member which fits into a first hollow bore in the central support member of the yoke. The capo also includes a substantially Y-shaped saddle member having a stem which slidably fits through a second hollow bore of the central support member, and an adjustment member for positioning the saddle member in the yoke. The engagement/release member is releasably held in position against the adjustment member by spring pressure. Rapid positioning of the saddle member is enabled by both coarse and fine adjustment of the adjustment member, made possible by buttressed threads present both inside of the engagement/release member and outside of a threaded shaft of the adjustment member.