The pen tube is a clarinet air-sounding instrument unique to the Buyi people, named for its slender shape similar to that of a writing brush.

The pen tube is composed of a tube body and a resonator, with a total length of 75 cm. The tube body is made of bamboo, and it is mostly made of locally produced water bamboo or fire tube bamboo (also known as pen tube bamboo) with thin tube, long section and thin wall.

The size of the pen tube varies. The more common one is 65 cm in length, 1.5 cm in outer diameter at the end, and 1.1 cm in inner diameter. The head of the tube is closed with a bamboo joint, the middle is transparent, and the end of the tube is open. Thin and flatten the 4 cm long tube wall under the first section of the tube, and use a sharp knife to carve a rectangular bamboo reed on it. , 0.6 cm wide. There are three circular sound holes on the front of the tube body, the diameter of which is 0.4 cm, and the distance between the holes is unequal. The resonance tube is made of half gourd, trumpet-shaped, and the tube is 13 cm long. Between the end of the tube and the resonator, there is also a silk strip as decoration.