A clasp for a bracelet or wristband includes first and second blades, the first blade being articulated to the second blade by a first end, between a closed position, in which the second blade is folded onto the first blade, and an open position, in which the second blade is released from the first blade, the first blade being articulated at a second end to a member for attaching a first wristband portion. The clasp includes an adjustment mechanism arranged to adjust the position of the second blade with respect to the first blade in an open position, the adjustment mechanism including a groove machined in the second blade, an arbor integral with the first blade and passing through the groove, the arbor receiving a pusher for releasing and/or locking it in order to move the second blade.