Bolts differ from screws in several ways. The most common difference is that bolts are used with nuts. The shaft of a bolt has an exterior spiral threading and a nut has an inner spiral threading. The two threadings match and allow the nut to tighten onto the bolt and hold objects together. Nuts and bolts allow the bolted together objects to be taken apart more easily, requiring only that the nut be unscrewed and then the bolt pulled loose.
Description
Some bolts are never used with nuts, and some bolts than can be used with nuts are not. This depends on the application or the objects being bolted together. Nut bolts are the types of bolts that can be used with nuts. Nut bolts have flat ends, rather than pointed ends, like screws.
Hex Bolts
Hex bolts are a type of nut bolt, or bolt used with nuts, that have hexagonal heads. The hex bolt may have spiral threading from the end of the shaft to the head, or a portion of the way up the shaft. Hex bolts can also be used in screw holes, though they cannot be screwed into wood unless a drilled hole already exists in the diameter of the bolt. Hexagonal closed or open-ended nuts are used most often with this type of bolt.
Carriage Bolt
Nuts are used to fasten off the open end of carriage bolts, which are bolts that have rounded heads. Directly underneath the rounded head is a square or polygon section used to make the bolt more easily removed. Carriage bolts are used with various types of nuts, though rounded or domed nuts like the cap or acorn nut are used most often.
Shaped Bolts
Shaped bolts like the J-bolt, U-bolt, or eyebolt are designed with flat ends for use with bolts. These types of bolts are used for tie-downs, attaching ropes and holding several objects together, or securing objects to a wall. The U-shaped bolt uses a special double-hole washer and hexagonal nuts to create a D-ring for holding objects together or holding a pipe to a surface.
Nuts
Nuts for bolts are available in different varieties. Some nuts are closed at an end, while others are open for optimal tightening to push two objects as close together as possible. Notched nuts like the slotted, castle, tee or kep nuts. The wing nut has two little handles to allow tightening and loosening by hand. Another type of nut, known as the coupling nut, allows headless bolts of other threaded rots to be pieced together.
