A magazine has a plurality of storage ports 400 each of which retains a stylus module 314 for use in measuring workpiece dimensions on a coordinate measuring machine. Each storage port 400 is configured as a pair of jaws provided by docking inserts 414. A permanent magnet 418 is mounted on each docking insert 414. The lower casing of the stylus module 314 is urged against the inwardly facing edges 416 of the docking inserts 414 by the magnetic attraction force due the magnets 418. The stylus module 314 is engaged with a retaining module (on the quill of the machine) by moving the retaining module in a downward sense to engage the stylus module 314; further downward movement disengages the stylus module 314 from the storage port 400, thus enabling engagement of such a stylus module and removal of the module from the storage port in a single continuous movement.