Abstract: Rings formed as slitter knives or counter-members are secured against axial displacement from selected positions along a slitter roller by inflating a number of pneumatic tubes carried in recesses formed in the circumferential surface of the roller, the recesses running lengthwise of the roller and being all located on one side of a plane containing the rotational axis of the roller. A flat is formed on the roller at a position diametrically opposite the pneumatic tubes to provide more positive location of the rings. Air is supplied to the tubes via a hollow shaft fitted to one end of the roller, the tubes being in pairs each formed from a tube of U-shape, the legs being disposed in adjacent recesses one end being connected to the hollow shaft and the other closed. Balancing of the roller is obtained by the use of different length set screws to which different numbers of washers are fitted, and also weights may be fitted to the inside of the roller.