31. The numbers marked with dimensions are called the dimension basis. Machine parts have at least one dimension reference in each of the three directions of length, width, and height.

32. The five elements of a thread are thread profile, diameter, pitch, lead, number of threads, and direction of rotation.

33. Only when the tooth shape, diameter, pitch, number of threads, and direction of rotation of the inner and outer ribs are consistent, can they rotate together.

34. A standard thread is one in which the tooth shape, diameter, and pitch of the thread comply with national standards. Non standard threads that do not meet national standards are referred to as non-standard threads. Special threads are those whose tooth shape meets national standards, but whose diameter and pitch do not meet national standards.

35. The prescribed drawing method for external threads is: the major diameter is represented by _________, the minor diameter is represented by _________, and the termination line is represented by a thick solid line.

36. In the sectional view, the major diameter of the internal thread is represented by ______, the minor diameter is represented by ______, and the termination line is represented by a thick solid line. Invisible threaded holes, their major diameter, minor diameter, and termination line are all represented by thick solid lines.