Abstract: A one-piece pull-tight or strap-type security seal adapted for closing bags or the like that is designed to be easily applied in comparison with existing ones. One seal of this type has a lever operation in which a closure strap (4) is integral with a central or operating portion (2) that is, its turn, integral with a lever member (6) to which the strap may be fixed during application around the neck of a bag to be closed. The lever member is then pivoted outwardly and backwardly over the operating portion, tightening the loop so formed by means of a lever action, and then locked by security locking formations (16, 19) to effect sealing. According to the invention, the closure strap is for all effects flat, its formations for fixing it to the lever member (6) comprising a series of orifices (7) distributed along its length, whereas the immobilising formation for the closure strap comprises a first protuberance (15) adapted, on formation of the loop (25), to be received in one of the said orifices (7).