Countersunk head bolts with slot

If you want a smooth component surface, protruding bolt heads are not so popular. Before the invention of the hexagon socket, the most common head design for countersunk bolts was slotted. Although the slot is easy to handle with standard screwdrivers, the slot can gouge the countersunk hole if it is not deburred. Another disadvantage is the low torque that can be transferred with a slot and boltdriver.

For countersunk bolts with imperial dimensions, the diameter and pitch are specified in fractions of an inch (25.4 mm) and threads per inch. In contrast to metric countersunk head bolts, the countersinking angle is also smaller: 82° is common. The specified length is the total length including the head.