Originally Posted by
Jim Dawson
The real advantage of the ER system is that the collets have a gripping range of about 1mm, which means you can use them to hold drill bits of any size. The MT2 endmill holders are limited to standard sizes, typically 1/8 to 1/2 by 16ths. However endmill shank sizes are in increments of 16ths also. 3/16, 1/4, 3/8, and 1/2 being the most common in the sizes you would be using on that mill. The advantage of an endmill holder is that the endmill is secured with a set screw that fits into the flat on the endmill. Prevents pullout and spinning in the holder. ER collets or any collet for that matter relies on friction to hold the cutter, normally this works just fine except in the case of really heavy cutting.