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BT40 SK Collet Chuck Tool Holders
What are the differences between SK and ER Collet Systems?
ER collets have an included angle of 16 degrees and most collets have a range of 1mm. Grip is strong and in most applications sufficient.
SK collets have an included angle of 8 degrees and most collets have a range of .5mm. Grip is very strong and is a step above ER collets. More of the collet sits in the taper pocket so concentricity is equal or better than ER collets.