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4.4.3 SCREWS

Screws are used where bolts are inconvenient to use. In the case of screws, the threads on the
shank are continued to a distance from the head of the screw not exceeding two times the pitch of
the thread for diameter up to 25 mm.
A screw is a threaded bar on the first side and a head of different forms on the second. Figure
4.18, a shows а countersunk head screw accoding to State Standard 17475:2008, and figure 4.18, b
shows а cheese-head screw accoding to State Standard 1491:2008. The metrical thread of coarse or
fine pitches with the tolerance zone 6g and 8g is done on a screw. As a rule, on a screwhead spline
under a screwdriver is done. The basic parameters of countersunk head screws and cheese-head
screws are resulted in table 4.5.

а) b)
Figure 4.18 – Screws.
The example of denotation of countersunk-head screw, with accuracy A, type 2, threads
diameter 12 mm, a coarse pitch, length 45 mm, tolerance zone 8g, the strength class 5,8 without
coverage:
Screw A2.M1245-8g.58 State Standard 17475:2008
Basic parameters of countersunk-head screws are resulted in table 4.5, and cheese-head
screws are resulted in table 4.6.

Table 4.5
Nominal thread Pitch of thread D H b h c L Length l 0
diameter depending on l*
d n, mm
coarse fine l 0 l*
12 1.75 1.25 21.5 6 3 2.5 1.6 22-85 30 42-85
14 2 1.5 25 7 3 3 1.6 25-90 34 47-90
16 2 1.5 28.5 8 4 3.5 2 30-95 38 55-95
18 2.5 1.5 32.5 9 4 4 2.5 35-100 42 59-100
20 2.5 1.5 36 10 5 4.5 2.5 40-110 46 65-110

Table 4.6
Nominal Pitch of thread D H b h c r L Length l 0
thread depending on l*
diameter
d n, mm coarse fine l 0 l*
12 1.75 1.25 18 6 3 2.5 1.6 0.6 22-85 30 35-85
14 2 1.5 21 7 3 3 1.6 0.6 25-90 34 40-90
16 2 1.5 24 8 4 3.5 2 0.6 30-95 38 45-95
18 2.5 1.5 27 9 4 4 2.5 0.6 35-100 42 50-100
20 2.5 1.5 30 10 5 4.5 2.5 0.8 40-110 46 55-110

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