man·drel or man·dril 
(măndrəl)
(măndrəl)n.
1. A spindle or an axle used to secure or support material being machined or milled.
2. A metal rod or bar around which material, such as metal or glass, may be shaped.
3. A shaft on which a working tool is mounted, as in a dental drill.
[Possibly alteration of French mandrin, lathe, from Provençal mandre, axle, crank, from Old Provençal, beam of a balance, from Latin mamphur, bow-drill, perhaps from Oscan.]