A hollow bar is always round and can look like a pipe or a tube, however, typically the walls are much thicker.
A hollow bar has the strength of a solid round bar, but since there is no center, there is less weight per foot which can sometimes save money, without compromising strength.
A hollow bar, depending on the application, can be machined both on the inside and the outside.
Hollow bars are measured by giving an inner diameter (ID) and outer diameter (OD).
