Because the thread uses a prescribed drawing method, the tooth profile of the thread and the size and accuracy requirements of each part cannot be marked on the graphics one by one. For this reason, national standards stipulate the design requirements for the use of thread marks to indicate threads. The complete thread mark is composed of the thread feature code, size code, tolerance zone code, and twist length code. See Table 6-1 for the marking methods of various common threads.
(1) Code and mark of common thread:
Characteristic code (M) Nominal diameter ′ Pitch — Single-line rotation direction (note left-hand code LH only)
Characteristic code (M) Nominal diameter x P h lead P pitch-multi-line
(2) Code and label of trapezoidal thread and zigzag thread:
Characteristic code (Tr, B) Nominal diameter ′ Pitch-Single line Rotation direction (note only left hand code LH)
Feature code (Tr, B) Nominal diameter ′ Lead (P pitch)-multi-line
(3) Code and marking of pipe thread:
Feature code (G, R c, Rp, R, NPT) Dimension code — rotation direction (note only left-hand code LH)
Among them, the letter G represents a 55 ° unsealed cylindrical (inner and outer) pipe thread, and Rc, Rp, and R represent 55 ° sealed conical internal threads, cylindrical internal threads, and conical external threads (the times of rotation with cylindrical internal threads It is R1, and the era number of conical internal thread is R2), NPT means 60 ° sealed conical (internal and external) pipe thread. It should be noted that the size code of the pipe thread is in inches, and its size is approximately equal to the diameter of the pipe with the external thread and not the large diameter of the pipe thread. In addition, the marking of pipe threads is drawn from the major diameter line of the thread with a guide line, and the guide line should not be parallel to the section line.
Example of thread marking:
“M16 ′ Ph3 P1.5—LH—5g 6g—L” means ordinary thread (external thread) with a nominal diameter of 16 mm, a lead of 3mm (without the value and symbol Ph on a single line), and a pitch of 1.5mm (a Note the symbol P, do not note the value for coarse teeth), left-hand (right-hand does not note), the tolerance zone of the middle diameter is 5g, the tolerance zone of the top diameter is 6g, the length of the long turn (the length of the turn is divided into L (length), N (medium ), S (short) three groups, medium spin length is not noted).
"Tr40'7-7H" means a single-line right-handed trapezoidal thread (inner spiral) with a nominal diameter of 40mm and a pitch of 7mm. The tolerance code for the middle and top diameters is 7H, with a medium twist length.
“B40′10 (P5) LH—8c” represents a zigzag thread (external thread), with a nominal diameter of 40mm, a pitch of 5mm, a lead of 10mm, a double-threaded thread, left-handedness, and the tolerance codes for the middle and top diameter 8c, medium twist length.