Abstract: A flange lock for securing a disk 8 on the spindle 10 of a power tool is described. It comprises a boss 11 screwable on the spindle and inner and outer flanges 4,1 non-rotatably mounted on said boss 11 so as to be relatively movable thereon between a first, separated relation rigid with said boss and a second, less separated relation. Separation balls 5 are mounted between the flanges 4,1 and disposable between a first condition in which the flanges are maintained in the first, separated relation and a second condition in which the flanges 4,1 are able to move relatively together to the second, less separated condition.