Best means to create new screw holes in models

www.McMaster.com        They have everything you need. Taps, Dies, Drills, and many, many types and sizes of screw fasteners.

Here are some links to an Industrial supplier for some small taps and dies that I use.

4-40 taps

4-40 dies

3-48 taps

3-48 dies

There are other larger and smaller taps and dies available also.

Here is a supplier of miniature fasteners I use.

Here is a tap drill size chart for reference.

Larry

You need to figure out what size hole you need based on what size screw you need.   Then pick a tap that makes the threads for the screw.   Then you get the "tap drill size" for the selected tap.     Mark the hole location and drill the hole.   Then use the tap to thread.    Remember to lubricate the tap with oil or it may break in the hole.   If the metal is hard or thick (not brass), turn the tap half a turn, then back off, then turn half a turn past where you were, and back off etc.    That allows the cutting teeth to clear and also helps avoid breaking the tap.   

2-56 screws are quite common in O Scale usage.   A 2-56 screw is very common and the tap drill is a #50.    0-72 and 0-80 are smaller common sizes.   I don't remember the tap drill sizes for these.     All have taps readily available.   Your local hobby shop should stock all these, most do.    You need a tap holder too, a large pin vise will do for these.

drilling and tapping gives you a stronger mount in my opinion than any glue, and is pretty easy to do.   

A die is use for threading the rod, you will not need one for this.   

  Aluminum should be dry cut, and broke most often despite the cut, lubing the fully cut top threads only on deep holes, will make it easier and leave threads unstressed and not overcut.

Brass's and steels sliver and break better on fine cuts. Cutting oil is a huge improvement over lube oil, but lube oil often beats dry on brass and steel.

  On fine thread like that, too much oil can cause excess clumping of slivers, on my fine holes& taps are are forced air cleaned often, tap re-oiled and the tip touched back on the cloth to soak dry excess oil welled in the flutes. 

Tap sets come with three different taps, each with a purpose.  There is a (1.) taper tap, (2.) bottoming  tap, and  (3.) a bottom finish tap.  Each designed to remove the material needed without breaking the tap, another huge problem.  You start with the taper tap, pictured, and finish with the top one, all the same size tap.  There is also a detail that indicates the size of hole required for the proper tap.  Some type, of a tap handle, or larger pin vise, to hold/turn the tap, is also a plus.  A fair amount of patients needs to be applied also.