unlike most other machine collet systems, 5c collets were developed primarily for work holding. superficially similar to r8 collets, 5c collets have an external thread at the rear for drawing the collet closed and so work pieces may pass right through the collet and chuck (5c collets often also have an internal thread for workpiece locating). collets are also available to hold square and hex stock. 5c collets have a limited closing range, and so shank and collet diameters must be a close match. a number of other c-series collets (1c, 3c, 4c, 5c, 16c, 20c & 25c) with different holding ranges also exist.