In the early 1960s, extruders typically had a length/diameter ratio of 20:1, and a machine with a 24:1 L/D was considered long. Since then, extruders have gotten longer, with the 30:1 to 36:1 L/D becoming the industry stan- dard. Some extruders even exceed 40:1 L/D for special purposes like double venting, compounding, or high-speed processing.