Carmex Single Long Carbide Shank Threading Insert holders - For Carbide External/Internal Threading Inserts - SR0021M21CIntroducing the Carmex SR0021M21C a single long carbide shank threading insert holder designed for CNC milling that handles both external and internal threading with precision. Built for long overhangs, it delivers reliable reach and consistent results in demanding machining environments. Internal coolant bore: Integrated coolant channel directs coolant to the cutting edge for better chip control and extended insert life. Long reach capability: