- High speed steel and cobalt end mills are used in applications where carbide may not be the best choice. Although the high speed steel tools are not as durable as the carbide end mills, HSS end mill bits are less brittle and have more ability to be run under less precise conditions where toolholding and workholding may not be as rigid or other limitation exist with the machine. High speed steel deflects more than carbide, especially as the projection from the toolholder increases. Due to the manufacturing process, special high speed steel end mills are not readily available. Many styles of high speed steel end mills have been discontinued, and can now be found ini our closeout section. In addition to the products you see here, we have a wide selection of high speed steel and cobalt end mills available. Please contact us for further informtion.