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Screws

1-10. Screws

Screws are another means of fastening one member to another. Screws have some advantages over nails. They have greater holding power, present a neater appearance, and have more decorative possibilities than nails. They also have the advantage of being easily removed or tightened.

a. Phillips Head. Screws are usually either slotted-head or Phillips head (Figure 1-33). Phillips head screws require a special screwdriver for driving them. Some advantages of Phillips head screws are that the screwdriver does not slip out easily and that the head is not as apt to break as that of a conventional type screw.

Figure 1-33. Slotted and Phillips head

b. Wood Screws. Wood screws are made of iron, bronze, brass, copper, or other metals; however, some are coated with nickel or chrome to match special-finish hardware. The main types of wood screws are roundhead, oval head, and flathead, which can be either slotted or Phillips head.

(1) Roundhead Screws. Roundhead screws (Figure 1-34) are usually used on a surface where the heads will show. The head is not countersunk, and for this reason it should have a pleasing finish-either blued or polished. If slotted-head, the screw slot should always be left in a parallel position to the grain of the wood.

Figure 1-34. Roundhead screw

(2) Oval-head Screws. Ovalhead screws (Figure 1-35) are used to fasten hinges or other finish hardware to wood. If slotted-head, the screw slots of these screws should be parallel to each other for better appearance.

Figure 1-35. Ovalhead screw

(3) Flathead Screws. Flathead screws (Figure 1-36) are used where the head will not show. The head should be countersunk until it is level with or slightly below the finished surface. If flathead screws are used on an exposed area, they should be countersunk in a hole that can be plugged.

Figure 1-36. Flathead screw

(4) Other Screws.

(a) Lag Screws. Lag screws are longer and heavier than the common wood screw and have coarser threads. They have square and hexagon heads (Figure 1-37). They are used when ordinary wood screws would be too short or too light and spikes would not be strong enough.

Figure 1-37. Lag screws

(b) Drive Screws. Special screws, made to be driven with a hammer, are called drive screws (Figure 1-38). They may have a roundhead but are usually made with a flathead, and they may have no slot for a screwdriver. (They also come in larger sizes with square or round heads.) The threads are far apart. Drive screws are available in the same size as wood screws.

Figure 1-38. Drive screw

(c) Special Screws. Many special hanging and fastening devices have a screw-type body (Figure 1-39). The screw eye is often used on picture frames, screen doors, and many other items. The curved screw hook and square screw hooks are mainly used for hanging articles. The curved screw hook is usually used in the ceiling, while the square screw hook is more often used on vertical walls.

Figure 1-39. Special screws

c. Sheet-Metal Screws. Like wood screws, sheet-metal screws can also be slotted or Phillips head. They are used for the assembly of metal parts. They are steel or brass with four types of heads: flat, round, oval, and fillister, as shown in Figure 1-40.

Figure 1-40. Sheet metal screws

d. Pilot and Starter Holes. Prepare the wood for receiving a screw by baring a pilot hole (the size of the diameter of the screw) into the piece of wood. A smaller, starter hole is then bored into the piece of wood that is to act as anchor or hold the threads of the screw. The starter hole has a diameter less than that of the screw threads and is drilled to a depth 1/2 or 2/3 the length of the threads to be anchored. This method (shown in Figure 1-41) assures accuracy in placing the screws and reduces the possibility of splitting the wood.

Figure 1-41. Sinking a wood screw

e. Covering Material. Both slotted and Phillips flathead screws are countersunk enough that a covering material can be used (Figure 1-42).

Figure 1-42. Screw-covering material

Curriculum design: David L. Heiserman
Publisher: SweetHaven Publishing Services