BOLTS AND NUTS

A bolt is fastening element comprising of the head at one end a threaded portion over a cylindrical shank at the other end. The parts to be fastened temporarily by bolts and nuts admit hexagonal head and Square head are very common. although the square shape provides a better spanner grip than the hexagon, but needs one fourth of a turn to bring it into the same position for inserting the spanner again whereas a hexagon need only one sixth of a turn and hence preferred.
the bolts through the holes in them having suitable clearance. The projected threaded end of the bolt in turn now admits the washer and nut an internally threaded member, which after sufficient turn offers necessary clamping grip. Bolts and nuts of various shapes are used fir different purposes but the 

     

Empirical Proportions of Hexagonal Head Bolt and Nut

All Dimensions in mm                                                                                                                                                                      
                                                                      Approximate proportion in

                 Detail                                                         Terms of d

                                                                                                                                                                                                                                               

Diameter of the bolt                                                                d

Width across corners of bolt head or nut                               2d

Width across flats of bolt head or nut                           1.5d+3 or 1.25d+6

Root diameter                                                                d-1.23 pitch

                                                                                          (Accurate)

                                                                                                  Or

                                                                                                 0.8d

                                                                                        (Approximate)

Thickness of bolt head                                                            0.8d

Thickness of nut                                                                      0.9d

Conical chamfer                                                                       30˚

Radius of the spherical end of the bolt                                    d

Thread run out                                                                     2.5 pitches

                                                                                          (Accurate)

                                                                                                Or

                                                                                                0.8d

                                                                                        (Approximate)

Empirical Proportions of Square Head Bolt and Nut

All Dimensions in mm                                                                                                                                                                                                

                                                                       Approximate proportion in

                 Detail                                                      Terms of d

                                                                                                                                                                                                                                               

Diameter of the bolt                                                                d

Width across corners of bolt head or nut            √2x (width across flats)

Width across flats of bolt head or nut                      1.5d +3 or 1.25d+6

Thickness of bolt head                                                        0.8d

Thickness of nut                                                                  0.9d

Conical chamfer                                                                    30˚

Radius of the spherical end of the bolt                                    d

Thread run out                                                     2.5 pitch    (accurate)

                                                                             0.4d     (approximate)

Chamfering of Bolt Head and Nuts:

The sharp hexagon or square corners of the bolt head and nut are removed by chamfering conically at 30˚ to the flat end face of the bolt head or nut. The bolt head being chamfered only on the upper face. While the nut is chambered either on only one face on both faces. Although the curves produced by the bolt heads and nuts are hyperbolas. But in practice these curves are always represented approximately by circular arcs. The methods of drawing these arcs.

Drill Sizes for Threaded Holes

All dimensions in mm

Sizes of The threaded Hole	Pitch	Drill Size d₁	Sizes of The threaded Hole	Pitch	Drill Size d₁
M 1	0.25	0.75	M 14	2	12
M 1.1	0.25	0.85	M 16	2	14
M 1.2	0.25	0.95	M 18	2.5	15.5
M 1.4	0.3	1.1	M 20	2.5	17.5
M 1.6	0.35	1.25	M 22	2.5	19.5
M 1.8	0.35	1.45	M 24	3	21
M 2	0.4	1.6	M 25	3	22
M 2.2	0.45	2.05	M 27	3.5	26.5
M 3	0.5	2.5	M 33	3.5	29.5
M 3.5	0.6	2.0	M 36	4	32
M 4	0.7	3.3	M 39	4	35
M 4.5	0.75	3.75	M 42	4.5	37.5
M 5	0.8	4.2	M 45	4.5	40.5
M 6	1	5	M 48	5	43
M 7	1	6	M 52	5	47
M 8	1.25	6.75	M 56	5.5	50.5
M 10	1.5	8.5	M 60	5.5	50.5
M 12	1.75	10.25	M 64	6	58
CONTINUED NEXT COLUMM			M 68	6	62

Different types of “V” threads

B S W Thread:-British Standard Whitworth.

This thread was introduced by Sir Joseph Whitworth and was standardized as British standard thread abbreviated as BSW. The profile of this thread with standard proportions. It has a thread angle of 55 and is rounded off at the crest and root as to render it less liable to damage sharp V Thread.

B S F Thread: - British Standard fine.

The profile of this thread is similar to that of BSW, but pitches are closer and hence the depth of the thread will be small. This has a better finish comparatively. These are commonly used in aircraft and automobile work.

B S P Thread: - British Standard pipe.

          This thread is also similar to BSW profile with finer pitches so as to suit the wall thickness and the material of the pipe.

B A Thread: - British Association.

          This thread was standardized by British association and used extensively for small screws used for electrical and other instrument work. The profile of this thread with standard proportions. It has a thread angle of 47.5˚.  

SELLERS Thread:-American national.

This thread was adopted as the American standard thread by the American standards institution. The profile of this thread with standard proportion. It has 60˚ thread angle and crests and root are kept flat.

UNIFIED Thread:-ISO Metric Thread.

The Indian standard institution has adopted V-thread profile recommended by the international organization for standards ISO metric screw thread for use in this country. This thread is also known as unified thread. It has 60˚ thread angle. The profile of this thread with standard proportions.

 A washer is a cylindrical piece of metal with a hole toreceive the bolt. It is used to give a perfect seating forthe nut and to distribute the tightening force uniformlyto the parts under the joint. It also prevents the nut from damaging the metal surface under the joint.a washer, with the proportions marked. illustrates the views of a hexagonal headed bolt with a nut and a washer in position.