1 mm. The pitch of optical fiber butt joint is M8x 1, where m stands for metric thread, 8 stands for thread diameter, and 1 stands for pitch. The specific dimension is 8mm in diameter, and the tolerance is negative 0.046mm to positive 0.082mm; the pitch is 1mm, and the tolerance is -0.050mm to-0.071mm.. This standard pitch is characterized by simple thread structure, convenient processing and wide application range. This standard is often used to handle optical fiber butt joints in optical communication and optical fiber transmission equipment to ensure the reliability and stability of the connection.