Suggestions for Tight Bakelite Knobs?

[Dubis7]

I finally picked up some replacement knobs for my Zenith FM radio. These have been a bear to find. Unfortunately, the new knobs appear to have shrunk a bit, and won't fit over the power/volume pot shaft. I don't want to try and force them and risk damaging one. Does anyone have any suggestions to make the plastic flex enough to fit over the shaft? Last resort I could probably sand away some of the interior shaft, but I don't know if there are any other approaches that wouldn't risk damaging the bakelite.