Abstract: An adjustable clasp comprises a retainer body having an elongate cavity within which slides a strap having saw teeth. The retainer body includes a main generally non-deformable body from which extends a flexible tongue provided with pawls projecting into the cavity to engage the teeth of the strap, and at least one resilient wing facing the flexible tongue and engagable under pressure to disengage the pawls from the teeth of the strap. The retainer body has guide members on the main portion and second guide members close to the opposite end of the main body, to maintain the strap close to the pawls. The second guide members include a contact portion extending from the resilient wing at its end opposite the main portion of the retainer body.