37. Common forms of threaded connections include bolt connections, double headed screw connections, and screw connections.

38. The types of commonly used keys include regular flat keys, half round keys, hook head wedge keys, and splines.

39. Cylindrical gears can be divided into straight teeth, helical teeth, and herringbone teeth according to the direction of the gear.

40. The prescribed drawing method for the gear tooth section is: the tooth top circle is drawn with a thick solid line; Draw the dividing circle with a fine dotted line. The tooth root circle can be drawn with thin solid lines or omitted. In the sectional view, the tooth root circle is drawn with thick solid lines.

41. When all surfaces of the parts have the same surface roughness requirements, they can be uniformly marked in the upper right corner of the drawing; When most of the surface roughness of the part is the same, the same roughness code can be marked in the upper right corner and the remaining two words can be added in front.

42. A complete assembly drawing should have the following four parts: ① A set of views. ② Necessary dimensions. ③ Technical requirements. ④ Part number and detail list.