Here are the maximum basic major diameters of small screws. The major
diameter is the size of the screw after threads have been cut. It’s
not uncommon to find screws with the major diameters .000-.010"
smaller than these.
0 - 0.060
1 - 0.073
2 - 0.086
3 - 0.099
4 - 0.112
5 - 0.125
6 - 0.138
8 - 0.164
Generally speaking, the wire being threaded should be within +0.000 &
-0.010 of the listed sizes. If the wire is larger than the listed
sizes, it’s difficult to get a smooth thread. If the wire is more than
0.010 undersize, the thread can be stripped easily when it’s tightened
in a nut or other threaded receptacle.
It’s quite difficult (if not impossible) to find commercial taps &
dies for the odd numbered sizes. Most industrial tool suppliers carry
these taps & dies.
A little lubricant on the wire helps when cutting threads. If the
wire to be threaded is soft, the area to be threaded can be hardened a
little by grasping the end in a pin vise or pliers, hold the portion
just beyond the threaded portion with another pliers & pull or twist
the pin vise or first pliers. A little practice on some scrap wire
will simplify the job & reduce the anxiety level.