Bolts

Bolts are used in construction requiring great strength or when the work under construction must be frequently disassembled. Their use usually implies the use of nuts for fastening and sometimes the use of washers to protect the surface of the materials they fasten. Bolts are selected for application to specific requirements in terms of length, diameter, threads, style of head, and type. Proper selection of head style and type of bolt results in good appearance as well as good construction. The use of washers between the nut and a wood surface or between both the nut and the head and their opposing surfaces helps you avoid marring the surfaces and permits additional torque in tightening.

Carriage Bolts

Carriage bolts fall into three categories: square neck, finned neck, and ribbed neck. All three are shown in Figure 52.

These bolts have round heads that are not designed to be driven. They are threaded only part of the way up the shaft. Usually, the threads are two to four times the diameter of the bolt in length. In each type of carriage bolt, the upper part of the shank, immediately below the head, is designed to grip the material in which the bolt is inserted and keep the bolt from turning when a nut is tightened down on it or removed. The finned type is designed with two or more fins extending from the head to the shank. The ribbed type is designed with longitudinal ribs, splines, or serrations on all or part of a shoulder located immediately beneath the head. Holes bored to receive carriage bolts are bored to be a tight fit for the body of the bolt and counterbored to permit the head of the bolt to fit flush with, or below the surface of, the material being fastened. The bolt is then driven through the hole with a hammer. Carriage bolts are chiefly for wood to wood application, but they can also be used for wood to metal applications. If used for wood to metal application, the head should be fitted to the wood item. Metal surfaces are sometimes predrilled and countersunk to permit the use of carriage bolts metal to metal. Carriage bolts can be obtained from 1/4 inch to 1 inch in diameter and from 3/4 inch to 20 inches long (Table 14). Use a common flat washer with carriage bolts between the nut and the surface.

Machine Bolts

The machine bolts shown in Figure 53 are made with cut national fine and national coarse threads extending in length from twice the diameter of the bolt plus 1/4 inch for bolts less than 6 inches in length to twice the diameter of the bolt plus 1/2 inch for bolts over 6 inches in length.

They are precision made and generally applied metal to metal where close tolerance is desirable. The head may be square, hexagonal, rounded, or flat countersunk. The nut usually corresponds in shape to the head of the bolt with which it is used. Machine bolts are externally driven only. Selection of the proper machine bolt is made on the basis of head style, length, diameter, number of threads per inch, and coarseness of thread. The hole through which the bolt is to pass is bored to the same diameter as the bolt. Machine bolts are made in diameters from 1/4 inch to 3 inches and may be obtained in any length desired, as shown in Table 15.

Stove Bolts

The stove bolts shown in Figure 54 are less precisely made than machine bolts.

They are made with either flat or round slotted heads and may have threads extending over the full length of the body, over part of the body, or over most of the body. They are generally used with square nuts and applied metal to metal, wood to wood, or wood to metal. If flatheaded, they are countersunk. If roundheaded, they are drawn flush to the surface.

Expansion Bolts

The expansion bolt, shown in Figure 55 is a bolt used in conjunction with an expansion shield to provide anchorage in substances in which a threaded fastener alone is useless. The shield, or expansion anchor, is inserted in a predrilled hole and expands when the bolt is driven into it. It becomes wedged firmly in the hole, providing a secure base for the grip of the fastener.

Toggle Bolts

The toggle bolt, shown in Figure 56, is a machine screw with a spring action, wing head nut that folds back as the entire assembly is pushed through a prepared hole in a hollow wall. The wing head then springs open inside the wall cavity. As the screw is tightened, the wing head is drawn against the inside surface of the finished wall material. Spring action, wing head toggle bolts are available in a variety of machine screw combinations. Common sizes range from 1/8 inch to 3/8 inch in diameter and 2 inches to 6 inches in length. They are particularly useful with sheetrock wall surfaces.

Molly Bolts

The molly bolt or molly expansion anchor, shown in Figure 57, is used to fasten small cabinets, towel bars, drapery hangers, mirrors, electrical fixtures, and other lightweight items to hollow walls. It is inserted in a prepared hole. Prongs on the outside of the shield grip the wall surfaces to prevent the shield from turning as the anchor screw is being driven. As the screw is tightened, the shield spreads and flattens against the interior of the wall. Various sizes of screw anchors can be used in hollow walls 1/8 inch to 1 3/4 inches thick.

Driftpins

The driftpin, shown in Figure 58, is a long, heavy, threadless bolt used to hold heavy pieces of timber together. It has a head that varies in diameter from 1/2 to 1 inch and in length from 18 to 26 inches. The term driftpin is almost universally used in practice. For supply purposes, the correct designation is driftbolt.

To use the driftpin, make a hole slightly smaller than the diameter of the pin in the timber. Drive the pin into the hole. The compression action of the wood fibers holds the pin in place.