ER-Style mill extensions enable micro tools to clear fixturing, maintain exceptional TIR at extended lengths, and solve deflection and chatter issues. They twist and snap into MOST standard ER clamping nuts, and limit TIR to <0.0002in at extension. Set screws hold small shank tooling securely in a triangular arrangement for excellent accuracy. An internal stop can be adjusted from both ends of the holder using a standard hex key to fine-tune stick out.