Screwed Fasteners 83
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d:\N-Design\Des5-1.pm5 Seventh Print
It may be noted from Fig. 5.7, that the crests of threads are indicated by a continuous thick
line and the roots, by a continuous thin line. For hidden screw threads, the crests and roots are
indicated by dotted lines. For threaded parts in section, hatching should be extended to the line
defining the crest of the thread. In the view from side, the threaded roots are represented by a
portion of a circle, drawn with a continuous thin line, of length approximately three-quarters of
the circumference.
The limit of useful length of screw threads is represented by a continuous thick line or a
dotted line, depending on its visibility. The length upto which the incomplete threads are formed
beyond the useful limit, is known as a run-out. It is represented by two inclined lines.
The simplified representation, though it saves time, is not an effective method to convey
thread forms. The schematic representation, used for the purpose is shown in Fig. 5.8. In practice,
the schematic representation is followed for only visible threads, i.e., for external threads and
internal threads in section. From the Fig. 5.8, it may be observed that the crest diameters, both
in external and internal threads, are drawn by thick lines. Further, the crests are represented by
thin lines, extending upto the major diameter and the roots by thick lines, extending upto the
minor diameter, these lines being drawn inclined with a slope equal to half the pitch.
Fig. 5.7 Conventional representation of threads