How many tubulins link to form single hollow tube of microtubule?

The correct answer is: 13

• There are a total of 13 tubulin links that are required to form a single hollow tube of the microtubule.
• The microtubule is referred to as one of the three fibers of the cytoskeleton. It is the thickest and is responsible for providing rigidity and support to the cells. It is also known for creating a passage that allows the movement of various cellular organelles. 
• Microtubules are made up of tubulin protein. Initially, a number of dimers are formed between the alpha and beta tubulin. In later stages, these dimers combine together and arrange themselves in form of a chain called the protofilament. 
• Then, the13 protofilaments join together and arrange themselves in the shape of the cylinder to form a microtubule. 

The protofilament and links arrange cylindrically to give the shape of a tubule which then, work as a passage for the organelles.