1. Hydraulic Collet type clamping system. 2. Hydraulic turning mandrel. 3. Hydraulic collet type chuck. 4. Hydraulic solid type gear shaving mandrel. 5. Hydraulic gear grinding mandrel. 6. Hydraulic gear shaping mandrel / fixture 7. Hydraulic OD grinding mandrel. 8. Hydraulic ID grinding mandrel. 9. Hydraulic hob grinding mandrel. 10. Hydraulic Gear Shaving mandrel. 11. Hydraulic Gear Hobbing Fixture. 12. Hydraulic Cylindrical grinding mandrel. 13. Hydraulic testing / Inspection mandrel 14. Balancing mandrel. 15. Hydraulic mandrel / collet for special application. The most common type of collet grips a round bar or tool, but there are collets for square, hexagonal, and other shapes. In addition to the outside-holding collets, there are collets used for holding a part on its inside surface so that it can be machined on the outside surface (similar to an expanding mandrel). Furthermore, it is not uncommon for machinists to make a custom collet to hold any unusual size or shape of part. These are often called emergency collets (e-collets) or soft collets (from the fact that they are bought in a soft (unhardened) state and machined as needed). Yet another type of collet is a step collet which steps up to a larger diameter from the spindle and allows holding of larger workpieces. The precise, symmetric form and rigid material of the collet provide precise, repeatable radial centering and axial concentricity. The basic mechanism fixes four of the six degrees of kinematic freedom, two locations and two angles. Collets may also be fitted to precisely align parts in the axial direction (a fifth degree of freedom) with an adjustable internal stop or by a shoulder stop machined into the internal form. The remaining sixth degree of freedom, namely the rotation of the part in the collet, may be fixed by using square, hexagonal, or other non-circular part geometry.