It is ER40 precision spring collet. Model: ER11. 1pc ER32 Precision Spring Collet. 1pc ER25 Precision SpringCollet. 1pc ER16 Precision Spring Collet. 1pc ER20 Precision Spring Collet. The insertion length of the tool should not be less than 2/3 of the clamping length of the chuck, otherwise the tool may deform the chuck, and may also lead to poor accuracy and breakage of the tool.
eBay