A 3k plain weave carbon fiber tube is a cylindrical structure made of carbon fiber fabrics that have been woven together in a 3k plain weave pattern. This type of weave is characterized by the carbon fibers passing over and under each other in a simple crisscross pattern. The 3k in the name refers to the number of individual fibers in each strand of carbon fiber, with 3k indicating a strand of 3,000 individual fibers.