A capo for a musical instrument includes a yoke with a center section and two opposed branches. A clamping bar, pivotally connected to one yoke branch, includes an engaging boss which fits into a machined notch of a second yoke branch, to releasably lock the clamping bar between the branches of the yoke. A resilient, string-contacting member is located on the main body of the clamping bar. The yoke's center section has a central bore therein with a non-circular cross section which may be X-shaped, and also has a hollow passage extending in a direction which is perpendicular to an axis of the central bore. A saddle member has a central stem extending through, and configured to slidably fit into the yoke's central bore, and a seat is attached to the stem. An adjustment member is provided for adjusting a position of the saddle member on the yoke.