Proxxon 28940 Set of MICROMOT Steel Collets, 6-Piece set comes in a practical holder for safe storage along with one clamping nut Proxxon micromot steel collets are hardened and have high, consistent flexibility so they maintain their accuracy with frequent use Triple slit collet offers substantially better load bearing surface than the easier to produce 4 slit type; important for small shank diameters