Locking block system to block movement of tensioner chain

The invention concerns a turnbuckle with a housing (1) which comprises a guide element (10) for a tension chain (11) running thereover. A detent pawl (2), which can pivot between an opening position and a locking position, is pre-tensioned against the guide element (10), and comprises a projecting nose (6) by means of which the tension chain (11) can be blocked against its tensioning direction. The turnbuckle further has a slot (20) which extends laterally on the housing (1) over the entire height thereof and through which the tension chain (11) can be introduced into the housing (1) and laid on the guide element (10). The nose takes the form of a shaped projection (6) which can be introduced into the space between two longitudinal legs (12') of a link (12) of the tension chain (11) and, with its leading face oriented in the direction towards the blocking position, forms a substantially rectilinear extension of the outer face (8) of a pawl leg (4) leading to the pivot pin (3) of the detent pawl (2). The nose (6) is provided with a central guide groove (14) which extends into the outer face (8) of the pawl leg (4) and into which the outer face of a link (12) of the tension chain (11) can be inserted at least partially.