These end mill collets have the unique ability to grip over a diameter range of 1mm without any loss of accuracy. This flexibility means that fewer collets need to be stocked, making them a more economical proposition when compared to other collet-based systems. An additional benefit is that there is no requirement for a separate imperial listing; a 1/4" end mill, for example, will fit into the 7mm to 6mm collet. Collet nuts are available separately, ideal for customers wishing to make their own holding devices or spindles. ER20 collet holders have M10 threads. Set of 12 comprises - 1 to 13mm.