Cap screws and machine screws
Cap screws and machine screws are similar in shape, differing only in their relative sizes. Machine
screws are usually smaller in size, compared to cap screws. These are used for fastening two
parts, one with clearance hole and the other with tapped hole. The clearance of the unthreaded
hole need not be shown on the drawing as its presence is obvious. Figure 5.24 shows different
types of cap and machine screws, with proportions marked
Cap screws are produced in finish form and are used on machines where accuracy and
appearance are important. As cap screws are inferior to studs, they are used only on machines
requiring few adjustments and are not suitable where frequent removal is necessary. These are
produced in different diameters, upto a maximum of 100 mm and lengths 250 mm.
Machine screws are produced with a naturally bright finish and are not heat treated. They
are particularly adopted for screwing into thin materials and the smaller ones are threaded
throughout the length. They are used in fire-arms, jigs, fixture and dies. They are produced in
different diameters upto a maximum of 20 mm and lengths upto 50 mm.