Custom nut driver for assembling quartz clocks

This nut driver is custom made forattaching and screwing down the hex nut that holds a mini quartz movement into the clock. It works on almost all movements that use an AA battery. 5/16" indicates the diameter of the shaft.  There are two sizes on this driver so it can accomodate different outside dimensions of the mounting nuts: Large and small.  It will not work on movements that use a C batterey.  Great time saver for clock manufacturers.