The world today length measurement unit there are two major kinds, a kind of the metric system for measuring unit, for m (m), cm (cm), mm (mm) and so on, in Europe, China and Japan, southeast Asia, and the other a used more for the imperial, measurement unit mainly for inches (inch), the equivalent of our country the old city ", in the us, the UK and the European and American countries use more.
1, the metric system of measurement: (10 into system)
1 m = 100 cm = 1000 mm
0 1 2 3 4 5 6 7 8 9 10 mm
2, the imperial measurement: (8 into system)
1 inch = 8 ft points 1 inch = 25.4 mm3/8 ￠￠x 25.4 = 9.52
1/16 3/16 5/16 7/16 9/16 11/16 13/16 15/16
0 1/8 1/4 to 1/2 3/8 5/8 3/4 inch 1 7/8
3, 1/4 ￠￠below with our products to said its call diameter, such as:
4 #, # 5, 6, 7, 8 # # # # # 12, 10,
The second chapter screw lines
A, thread is a kind of solid surface or the inner surface of section, there is even a raised shape. Spiral According to the structure characteristics and USES can be divided into three categories:
(a) the common thread: tooth shape of a triangle, and used for the connection or fastening parts. The common thread pitch divided into thick tooth in and fine tooth thread two kinds, fine tooth thread connection high strength.
(2) transmission thread: tooth shape have trapezoidal, rectangular, saw form and triangle, etc.
(3) seal thread: for sealing, mainly is the thread connection works, taper thread and tapered pipe threads.
Second, threaded with level:
Threaded screw thread with is close between loose or the size of the tight, cooperate with the level of the role is in the domestic and foreign threads deviation and tolerance of the provisions of the combination.
(A) to unite the imperial thread and outer thread has three thread level: 1 A, 2 A and 3 level A, threaded has three levels:
1 B, 2 B and 3 B level, is all clearance fit. The higher the rank, the digital with tight. In the imperial thread, deviation only 1 A and regulations A level 2, 3 A level of deviation is zero, and 1 A and 2 A level deviation is equal.
The greater the number of the smaller the tolerance level, as shown in figure:
1 B 2 B 3 B threaded
3 A male
1, 1 A and 1 B level, very loose, and its applicable to the tolerance level internal and external threads with tolerance.
2, 2 A and 2 B level, is the imperial series mechanical fasteners provisions of the most common thread tolerance level.
3, 3 A and B grade 3, combine to form the most tight spin with tolerance, apply to the tight fasteners, used for the safety of the key design.
4, foreign thread for, 1 A and 2 class A have A cooperate with tolerance, 3 level A no. 1 A level of tolerance than A grade 2 is 50% larger than the tolerance, 3 level A big 75%, the internal threads for, 2 B level tolerance than 2 A big 30% tolerance. 1 B level than 2 B level big 50%, more than 3 grade B big 75%.