LEGO and others sometimes calls those pieces [a "bearing element"][1]. This term however [is not limited to just that axle][2].

LEGO's replacement parts service calls the holes they go into "HOLE Ø11":

[![HOLE Ø11][3]][3]

The width of the axle is roughly equivalent to the width of a "bar", like [the 30374 piece][4] used for Lightsabers as such.

None of these names are particularly satisfactory, but I'm not aware of any better names.


  [1]: https://brickset.com/parts/448826/bearing-element-2x2-single
  [2]: https://brickset.com/parts/4211778/bearing-element-3x6
  [3]: https://i.sstatic.net/GAvCgm.png
  [4]: https://www.bricklink.com/v2/catalog/catalogitem.page?P=30374#T=C