ISO metric precision hexagon bolts, screws and nuts
are covered by BS 3643 and ISO 272. The standard
includes washer faced hexagon head bolts and full
bearing head bolts. In both cases there is a small radius
under the bolthead which would not normally be shown
on drawings, due to its size, but is included here for
completeness of the text. With an M36 bolt, the radius
is only 1.7 mm. Bolts may be chamfered at 45° at the
end of the shank, or radiused. The rounded end has a
radius of approximately one and one quarter times the
shank diameter and can also be used if required to
draw the rolled thread end. The washer face under the
head is also very thin and for a M36 bolt is only
0.5 mm.
Figure 16.1(a) shows the bolt proportions and Table
16.1 the dimensions for bolts in common use.
Dimensions of suitable nuts are also given and illustrated
in Fig. 16.1(b).
Included in Table 16.1 and shown in Fig. 16.1(c)
are typical washers to suit the above bolts and nuts
and these are covered by BS 4320. Standard washers
are available in two different thicknesses, in steel or
brass, and are normally plain, but may be chamfered.
Table 16.1 gives dimensions of commonly used bolts,
nuts and washers so that these can be used easily on
assembly drawings. For some dimensions maximum
and minimum values appear in the standards and we
have taken an average figure rounded up to the nearest
0.5 mm and this will be found satisfactory for normal
drawing purposes. Reference should be made to the
relevant standards quoted for exact dimensions if
required in design and manufacture.
Manual of
Engineering Drawing
Second edition
Colin H Simmons
I.Eng, FIED, Mem ASME.
Engineering Standards Consultant
Member of BS. & ISO Committees dealing with
Technical Product Documentation specifications
Formerly Standards Engineer, Lucas CAV.
Dennis E Maguire
CEng. MIMechE, Mem ASME, R.Eng.Des, MIED
Design Consultant
Formerly Senior Lecturer, Mechanical and
Production Engineering Department, Southall College
of Technology
City & Guilds International Chief Examiner in
Engineering Drawing
