Appliance for locking wheel rims for vehicles on repair workshop machines or the like, comprising: - supporting means associable with rotation means of a repair workshop machine or the like; - at least two locking jaws for locking the rim of a wheel which are associated with supporting means and moving along at least a direction of reciprocal moving close/away between a position of maximum opening, wherein said jaws are arranged at a maximum distance from each other, and a position of minimum opening, wherein said jaws are arranged at a minimum distance from each other; - movement means associated with said jaws and suitable for moving said jaws between said position of maximum opening and said position of minimum opening; - at least an adjustment device placed between said movement means and at least one of said jaws and suitable for adjusting said position of maximum opening and/or said position of minimum opening; - wherein said movement means comprise at least a self-centring system of levers (8, 9) connected to each of said jaws and suitable for keeping each of said jaws at the same distance to a central axis of rotation of said supporting means; characterized by the fact that said adjustment device comprises: - at least an adjustment element of a substantially elongated shape, associated with said movement means, revolving around its own longitudinal axis and having at least a threaded portion; - at least a mobile element associated integral with at least one of said jaws and having at least a threaded hole inside which is engaged said threaded portion of the adjustment element, the rotation of said adjustment element around said longitudinal axis being suitable for moving said mobile element on said threaded portion and along a direction of adjustment substantially parallel to said direction of reciprocal moving close/away. - supporting means associable with rotation means of a repair workshop machine or the like; - at least two locking jaws for locking the rim of a wheel which are associated with supporting means and moving along at least a direction of reciprocal moving close/away between a position of maximum opening, wherein said jaws are arranged at a maximum distance from each other, and a position of minimum opening, wherein said jaws are arranged at a minimum distance from each other; - movement means associated with said jaws and suitable for moving said jaws between said position of maximum opening and said position of minimum opening; - at least an adjustment device placed between said movement means and at least one of said jaws and suitable for adjusting said position of maximum opening and/or said position of minimum opening; - wherein said movement means comprise at least a self-centring system of levers (8, 9) connected to each of said jaws and suitable for keeping each of said jaws at the same distance to a central axis of rotation of said supporting means; - at least an adjustment element of a substantially elongated shape, associated with said movement means, revolving around its own longitudinal axis and having at least a threaded portion; - at least a mobile element associated integral with at least one of said jaws and having at least a threaded hole inside which is engaged said threaded portion of the adjustment element, the rotation of said adjustment element around said longitudinal axis being suitable for moving said mobile element on said threaded portion and along a direction of adjustment substantially parallel to said direction of reciprocal moving close/away.