W and O are mostly North American designations.
In general terms:
O grades = oil hardening = gauge plate
W grades = water hardening = silver steel.
We ran a very detailed article on hardening W and O steels in MEW, which all applied to gauge plate and silver steel (one of my hardest ever edits as I had to translate every temperature from Fahrenheit to Celsius and then check them all again).
American drill rod although being similar to silver steel lacks (manganese?) content that helps minimise distortion.
Neil