The labeling format of the thread mark is:
Thread code - thread tolerance band code (medium diameter, top diameter) - screw length
l) The tolerance band code is represented by a number plus a letter (the upper thread is used for upper thread and the lower thread is used for external thread), such as 7H, 6g, etc., it should be specially pointed out that 7H, 6g, etc. represent the thread tolerance, and H7, g6 represent the tolerance of the cylinder. Code.
2) The screw length is defined as three types: short (indicated by S), medium (indicated by N), and long (indicated by L). In general, the threaded length is not marked and the thread tolerance band is determined by the medium twist length (N). If necessary, add the screw length code S or L, such as "M20-5g6g-L". For special needs, indicate the value of the length of the screw, such as "M20-5g6g-30".