What is the best definition of a tube ligament?

A tube ligament refers specifically to the area between the tube holes on the tube sheet in a boiler or heat exchanger. This definition is essential because it highlights a crucial aspect of the tube sheet's design, which plays a significant role in both structural integrity and efficiency of heat exchange. Tube ligaments help to distribute stress and maintain the structural strength of the tube sheet, preventing potential failures caused by pressure or thermal expansion.

Recognizing this aspect is crucial for understanding how boilers operate and the importance of tube sheets in managing fluid flow and heat transfer. Other options may relate to components or functions of a boiler but do not capture the specific and technical nature of what a tube ligament is in the context of heavy machinery like boilers.