A door latch system (1) comprises a latch (10) and rose bases (60A,B) which clamp together against a door panel through a cross-drilling in the door panel by screws 80 engaging in bosses (94) above and below the latch body (12). The latch body is supported in the cross drilling by an adaptor (40) which in turn supports sleeve extensions (90) of the rose bases to prevent the rose bases from turning on operation of the handle knob/levers attached to the rose bases. The sleeve extensions are open, (that is, C-shaped in section) so that the diameter of the parts of the system within the cross drilling can be minimised, whereby the diameter of the rose bases can likewise be kept within desirable limits of size.