The three types of screws that we will focus on in this unit are wood, sheet metal, and machine screws.
Screws have a neat appearance and can be decorative. They have much more holding power than nails and can easily be removed without damaging the materials involved.
However, the cost factor of the screw and the time involved in installation must be considered.
Screws and Their Types
Click on each to find out more:
Wood screws are commonly made in 20 different stock thicknesses and lengths.
The two most common types of screw heads are slotted head and Phillips head. Screw heads may have any of several different shapes.
When using wood screws, it is generally necessary to drill pilot holes (particularly in hardwoods) to receive the screw. This does four things:
• Ensures pulling the materials tightly together
• Makes the screw easier to drive
• Prevents splitting the wood
• Prevents damage to the screw
Sheet Metal Screws
Sheet metal screws are thread-cutting or thread-forming screws used to fasten light-gauge sheet metal.
The threads of sheet metal screws are deeper than those of wood screws. This allows the two pieces of metal being fastened to be drawn tightly together.
Carpenters use machine screws to fasten butt hinges to metal jambs, or door closers to their brackets, and to install lock sets.
It is often necessary to drill and tap holes in metal to receive machine screws as fasteners for wood or various kinds of trim. Machine screws can be obtained with a straight slot or Phillips head.
Lag Screws and Shields
Lag screws or lag bolts are heavy-duty wood screws with square- or hex-shaped heads that provide greater holding power.
Concrete/Masonry screws are used to fasten a device or fixture to concrete, block, or brick. No anchor is needed.
Deck screws are made in a wide variety of shapes and sizes for different indoor and outdoor applications.
Some are made to fasten pressure-treated and other types of wood decking to wood framing. Self-drilling types are made to fasten wood decking to different gauges of metal support structures.
Drywall screws are thin, self-drilling screws with bugle-shaped heads.
Depending on the type of screw, it cuts through the wallboard and anchors itself into wood and/or metal studs, holding the wallboard tight to the stud.
Drive screws do not require the hole to be tapped. They are installed by hammering the screw into a drilled or punched hole of the proper size.
Hammer-Driven Pins and Studs
Hammer-driven pins or threaded studs use a special tool to fasten wood or steel to concrete or blocks, without the need to predrill holes.
Bolts are often used by the carpenter to attach one unit or member to another.
There are many different designs and types for special jobs, but we will discuss only the most common ones, in this module.
Bolts and Their Types
1. Stove Bolts:
Stove bolts come in either roundhead or flathead designs, with lengths ranging from 3/8 inch to 6 inch. The shanks are threaded all the way to the head, and are up to 2 inches long. If they are longer than 2 inches, they are threaded to a maximum of 2 inches.
They can be obtained in several different materials such as steel, brass, and copper. They are used in lighter types of construction assemblies.
1. Machine Bolts:
Machine bolts come with nuts. The nut is normally the same thickness as the diameter of the bolt. Specially designed nuts are obtainable for specific purposes such as self-locking, or cap nuts for safety or appearance.
2. Carriage Bolts:
The carriage bolt is similar to the machine bolt except for the design of the head. The head is oval and the shank is square. It is designed that way so that the bolt can be driven or drawn into the wood, and the nut tightened without the bolt turning.