megoodsen writes:

Can someone advise me the amount the rod (actually thick walled
tube-all relatively speaking of course) needs to be oversize to be the
right fit into the hole.

I think you mean a force fit, as given in Table 9 of _Machinery's
Handbook_, "ANSI Standard Force and Shrink Fits" in the chapter on
dimensioning. Not an "interference fit", which is for locating things, not
holding them, at least in ANSI and ISO terminology.

For sizes 0.24 to 0.40 inches and Class FN 1, the hole is oversize by 0 to
0.4 thou, the shaft by 0.5 to 0.74 thou, yielding an inteference of 0.1
to 0.75 thou. For Class FN 5 the values are hole 0 to +0.9, shaft +1.4 to
+2.0, inteference is then 0.5 to 2.0.

This two-page table gives the values for every possible class and size.

Have you considered knurling the shaft instead of force fitting? Doesn't
require holding such difficult tolerances on the machining.