[chrisguyw]

I too have wondered why NSR chose UNC4-40 instead of the slightly smaller M2.5 grub screw (M1.3 head)

As has been mentioned above Salvatore raced several classes of steel/scratchbuilt  cars for many years before he began producing plastic cars.
The standard at that time (worldwide, for slotcars) was UNC-40 set/grub screws, and he adopted this size in the NSR line of cars.

Ernies' chassis have been used off and on by many Wing/Eurosport racers......I did a review of his soon to be released 1/32 (home/club) chassis, elsewhere on this forum.

Cheers
Chris Walker

[Nonfractal]

Some useful information I did not include in the initial post above.
Most tap and die kits are supplied with a tap called a "taper" 
For most slot car wheels, the holes are (or can be drilled to be) 180 degrees apart. 
For the 180 degree wheels, the taper works fine because the tap has space to go right through the wheel collar and out of the other side.

However, some wheels have 3 screws set at 120 apart. 
If you use a taper on these wheels to try do complete your thread you will make a mess of it.
You will either strip the thread as you tap it or create an incomplete thread that will lock the set screw as you insert it.

The solution is to use 2nd and 3rd taps to complete the thread. 
The "bottoming" tap is used as the last cut and can cut right to the bottom of the hole avoiding striiping the thread ot creating an incomplete cut that might permanently lock the screw into the hole.