Janser Green Box Straight Heavy duty Blades RWS006A These Heavy duty blades are popular with carpet fitters as these Janser green box blades are reputed to have a longer cutting life. These heavy duty blades are packed in 100s and sub divided into 20 blades per dispenser.These Janser heavy duty 60mm blades conform to the standard pattern design which means they will fit most cutting knives like the popular Dolphin carpet fitters knife as well as the Janser coloured knife.