I have a set of numerical punches which can used in two different ways -  hand-held or in a holder.  Of course, much better results can be achieved by using a holder.  This tool is used for stamping round pieces, such as dials. The tool serves to guide the punch, while holding the workpiece, and provision is  made for accurately  indexing the workpiece to the next location. 

Below is shown the punch holder held in a vise.  The scale and plastic gear provide for indexing. The gear is part of the set that came with my lathe, and for some applications, other sizes are used.   

The cylindrical  aluminum part was used for practicing the technique of attaining the right "touch" used when tapping the punch with the hammer. 

It makes sense to develop the skills on a practice piece before proceeding to the "real thing." 

The brass knobs are used for locking. The top knob fixes the upper holder, and the bottom knob is used to lock the shaft which holds the workpiece.

Letter size is 2.5mm high, 60mm long and 6mm square. 

The guide hole size of the holder is 6mm. And the size of the punch marker is little bit larger than the guide size, so a over sized part has been grinded. 

My stamping tools ( 0 to 9) are shown below.  Initially these stamps  fit too snuggly  in the holder, so they were ground slightly.