A stem includes a stem body, a column and a locking device. The stem body is provided with a perforation. The column is disposed at one end of the stem body and provided with a first aperture, the perforation is in communication with the first aperture. The locking device is disposed in the perforation and includes a clamping part, two sliding blocks and a first fixing member, the clamping part is located between the sliding blocks, and the first fixing member penetrates the clamping part and the sliding blocks. When the first fixing member moves toward the inside of the perforation, the first fixing member drives the sliding blocks to approach each other and squeeze the clamping part, such that the clamping part moves in a direction toward the first aperture. According to this, the assembly and disassembly procedures of the present invention are quite simple and easy to operate.