Nut M12-7H. 5.029 State Standard 5915:2008.

The basic parameters of nuts are resulted in table 4.4.

Table 4.4

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

Table 4.6

STUDS

Studs are cylindrical numbers threaded at both ends.

A stud is a threaded bar on first end for screwing up in one of connecting parts, and threaded for a screwing on a nut on the second. Studs are mainly used in cases, when bolts and screws of large length are irrationally used.

The length of a thread end of L₁, for screwing up in a part depends on durability of the material of this part (table 4.7). The working length of a stud - L equals the part of its endlessly length, which is screwed up in a part. The length of cutting of a thread on the working end of a stud - l₀ is determined by its nominal diameter and is identical to the length of cutting of thread on a bolt (see table 4.3)

Figure 4.19 – A stud

Table 4.7

The example of conventional denotation of a stud of normal accuracy for screwing up in the cast-iron part, with the diameter of a thread 16 mm, by the tolerance zone 6g, a working length 60 mm, a strength class 5.8, without coverage:

Stud M16´60-6g.58 State Standard 22034:2008.

A construction and sizes of studs of the general setting is regulated State Standards 22032:2008 – 22043:2008. The parameters of a metrical thread the same as for bolts, nuts and screws.

WASHERS

A washer is a cylindrical piece of metal placed between the nuts to provide smooth bearing surface for the nut to turn on. It spreads the pressure of the nut over a greater area. It also prevents the nut from cutting into the metal and thus, allows the nut to be screwed on more tightly. It is chamfered on the top of the flat surface.

A washer is a flat part with an opening without a thread. Plain, single coil spring washers and lock washers are the most widespread. Two types of plain washers are represented in fig.4.20. Basic parameters of plain washers according to State Standard 11371-78 are shown in table 4.8.

The example of conventional denotation of a plain washer (type 1) for a fixing part with a thread M20, with a thickness set in a standard (01), by coverage 01 (zinc with chromating) 6 mkm thick: