wheel 5 forces the locking or arrest member 13 into locking engagement with the locking cam 12 as indicated in fig1 and 4a when the adjustable spanner according to the present invention is employed for example the thumb of the operator may press in the pin 4 and move the jaws 2 3 towards one corner or point of a bolt head the tips of the jaws 2 3 being forced apart so that the jaws 2 and 3 open sufficiently i against the action of the spring 8 that they grasp about the sides or flats of the bolt head 15 under a pressure which is generated by the spring 8 as soon as the jaws 2 and 3 have exactly gripped the flats of the bolt head 15 key width the depression on the pin 4 is released whereupon the moving jaw 3 is immediately locked in accordance with the above description the adjustable spanner is now ready to begin work by turning the bolt 15 right or left handedly as required when a new turn is needed for example for reasons of space the jaws 2 3 need not be disengaged from the bolt head 15 but a new turn can always be made by pressing the pin 4 and releasing it when the shaft i has assumed the desired and intended position from which it follows that the present invention also acts in a manner similar to a so called ratchet handle a suitably graded gauge 19 is advantageously provided on one or both sides of the spanner whereby the present invention may also act and be employed as a self positioning measurement gauge the embodiment described in the foregoing and shown on the drawings illustrates that the adjustable spanner will be self adjusting as a.