The invention relates to a buckle for a strap designed for fastening an object, particularly for the heel strap of swim fins of the open heel type. This strap is provided with a sequence of transverse teeth on one of its sides and is adjustably connected, at least at one of its ends, to the object to be fastened, particularly to said fin, at one side of the footpocket, by means of the buckle, which comprises a strap-guiding member, extending on the non-toothed side of the strap, transverse thereto, and around which said strap end is folded and returned, and a movable strap-locking tooth, extending, transverse to the strap, on the toothed side thereof, in coincidence with the strap-guiding member, and cooperating, together with counteracting elastic means, with the strap teeth, in such a way that the strap is only allowed to slide freely, when subject to a manual pulling force exerted on the free returned end of the strap, towards tightening the strap, whereas the strap is prevented from sliding in the opposite sense, i.e. towards loosening it. The buckle also comprises hand-operated strap-releasing means, for moving the strap-locking tooth away from the strap-guiding member, against the action of the associated counteracting elastic means, to such an extent as to disengage the strap-locking tooth from the strap teeth and to allow the strap to slide freely in both senses as long as the manual action is exerted on the strap-releasing means.
Buckles of this type are known, in which all operating members, i.e. the strap-guiding member, the movable strap-locking tooth with the counteracting elastic means associated thereto and the manual strap-releasing means are provided on a single body, attached to the body to be fastened, and particularly on one side of the footpocket of the open heel swim fin. This known construction of the buckle has the drawback that, in order to let the strap slide with respect to the buckle towards quick loosening and for a longer segment, for example in order to unfasten quickly the fastened object, and particularly to unfasten the swim fin from its respective foot, the strap-releasing means have to be continuously manually operated all the while, for example by exerting pressure on a lever bearing the strap-locking tooth and being stressed by the associated counteracting elastic means. This prolonged manual action is inconvenient and at times even impossible, and engages a hand of the user, keeping it busy for a relatively long time, for example to contribute to the strap loosening and unfastenening operations.
U.S. Pat. No. 4.795.385 discloses a buckle of the type described hereinbefore, whereby the heel strap of a swim fin of the open heel type is attached to the fin at least at one end of the footpocket. This known buckle consists of a fixed part, connected to the fin, and of a detachable part, which bears all the operating members, i.e. the strap-guiding member, the strap-locking tooth, with the associated counteracting elastic means, and the manual strap-releasing means. The detachable part is connected to the fixed part by elastic snap coupling means, which may be uncoupled with a relatively simple and quick uncoupling operation, so as to cause the detachable part of the buckle, together with the corresponding end of the heel strap, to be completely separated from the fixed part of the buckle, and therefore from the fin. This known construction of the buckle, allowing to unfasten the fin quickly from the foot of the swimmer, has other drawbacks, including that of causing an end of the heel strap to be completely detached from its respective fin, so that the heel strap is anyway opened.
European patent application 0 687 484 discloses a buckle of the type described hereinbefore, designed to connect at least one end of the heel strap of an open heel swim fin, to the corresponding side of the footpocket. This buckle also consists of a fixed part, linked to the fin, and of a movable part which bears all the operating members, i.e. the strap-guiding member, the movable strap-locking tooth, with the counteracting elastic means associated thereto, and the manual strap-releasing means. These two parts of the buckle are connected by means of a strap-stretching lever interposed therebetween, which has its fulcrum on the fixed part and is articulated to the movable part. The strap-stretching lever may be manually overturned about 180.degree.0 about its fulcrum between an angular strap-stretching position, wherein its articulation to the movable part of the buckle is between the point in which the fixed part of the buckle is attached to the fin and the fulcrum of the strap-stretching lever on said fixed part, and an angular strap-loosening position, in which the articulation of the strap-stretching lever to the movable part of the buckle is on the opposite side with respect to the fulcrum of the strap-stretching lever. Although this known construction of the buckle allows the heel strap to be quickly loosened and, at the same time, the fin to be unfastened from the foot of the swimmer by simply manually overturning the strap-stretching lever, without detaching or opening the heel strap, it has the drawbacks of comprising a third additional part, consisting of a strap-stretching lever, and of requiring, for quick strap stretching and loosening operations, a certain clearance on the side of the foot, which is needed to overturn the strap-stretching lever, but not always available in practice. Moreover, the overturnable strap-stretching lever may be easily accidentally and unintentionally shifted to its strap-loosening position.