Scandinavian Round For use with ASSA Modular and Connect lock cases. The cylinder is fixed with four high security hardened steel screws, supplied with the accessory set. ASSA accessories must be used. 3911 - Single Cylinder (External)For use with ASSA Modular and Connect lockcases. 3913 - Single Cylinder (Internal)For use with ASSA Modular and Connect lockcases. 3912 - Double CylinderFor use with ASSA Modular and Connect lockcases.