Long Island Indicator Service has posted a calibration instruction
that contains good information about what to use for calibrations of micrometers, etc., and how to go about it. I am not affiliated with Long Island Indicator.
The first issue with using rods is their traceability to NIST. Is that established?
The second issue is sensitivity. Are they calibrated with a 10:1 resolution or better? That is a general "rule of thumb" when using transfer standards to do an accuracy check.
The third issue is the recommendation to check calibration over a measurement range. This can be done by wringing gage blocks together - can you do that with your rods?
These three considerations are in general why I do not personally recommend calibrating with a rod, though a pin such as Deltronic
may be part of the process IF it's kept quite safe from wear and damage.
How big are we talking about? I used to wring together gage blocks to calibrate 12 inch micrometers.