We have speced either O-1, which is an oil hardening drill rod, or A2, which is an air hardening drill rod. Drill rod was choosen because it is readily available in the precision size we need. Precision drill rod is usually speced at -0.0000" +0.0005", in other words, either on spec or slightly oversize. This is not to be confused with non-precision drill rod, which is just mill sized.
The need is not for a particular material. Virtually any alloy or stainless steel will work. We do not need to harden the pins. However, it makes sense to start with a precision product which will not need to be ground to size.
If anyone wants to quote using a material other than precision drill rod, feel free to do so. However, be advised that, although not called out in the print, by definition, the call for precision drill rod determines that the diameter of the pin be held to -0.0000" +0.0005".