This massive wooden knitting needle came as part of a kit. 20.0mm seems a little over precise. It might suggest that the diameter is precise to the nearest 0.1mm as measured with a micrometer screw gauge or Vernier callipers. It could mean precise to the nearest 0.5mm, as in 20.0mm not 20.5mm. That's where we need some steer in the form of stated precision, eg 20.0 +/- 0.1mm for example.
