Sherline 3083 4″ End Mill Holder Style Fixture Includes Tommy bar This blank fixture can be screwed directly onto the 3/4-16 thread of the Sherline spindle and then turned or milled to hold a part of your choice. It is made from a 1″ diameter 12L14 steel billet cut 4″ long. The pre-cut thread assures accurate re-seating on the spindle thread each time the fixture is used.