 Blanc applied these concepts to muskets, and used gauges and filing jigs to bring duplicate parts to interchangeability.The uniformity of the parts was achieved via cut-and-try methods, using jigs, gauges, and master models to guide hand filing (there was no true milling at the time, although rotary filing on lathes was not unknown).As each part was filed, it was repeatedly compared against a gauge or master model (one part declared the model for all others to compare with), and the natural ability of the eyes and hands to detect small differences, such as a slight step up or down from the master to the part, ensured sufficient interchangeability.