A mandrel is a shaft or bar that is inserted into a hole in your work to hold it in place during machining. Types of Mandrels• Expanding mandrels are slightly tapered with an expandable wedge for holding your work.• Plain mandrels are hardened with tempered steel bar-holding mechanisms. • Nut mandrels are straight mandrels with a thread at one end.Use of Mandrels• Lathes• Jewellery making for forming the perfect shape• Tube bending and formation• Mounting s gear blank or pulley between centres