Screws are the most common type of fasteners used in fixing or fitting various products. The screws are widely used in joining of tubi , valvole and in other applications. They are supposed to be one of the most versatile and powerful fasteners.
The basic purpose of a screw is for holding all sorts of things together, which include wood, plastic and metal. There are different varieties , made of different materials and in different sizes, that have been developed to maximize efficacy for particular applications. There are hundreds of options when you consider that screws come in different diameters and lengths.
- Alloy steel
- Mild Steel
- Acciaio inossidabile
- Aluminum etc.
Finishes on screws:
Available finishes on screws are as follows:
- Zinc Plated
- Zinc Yellow
- Hot Dip Galvanized
- Black Zinc
- White coating
- Black coating
- Black oxide
- Non-stick coating etc.
- Slotted Screw: They are the most common and perhaps the oldest variety of screws. This type of screw has a linear slot in the head and can be fixed using a standard (flat) screwdriver.
- Hex Screw: These screws do not have any slots or grooves. The head of the screw is hexagonally shaped. These screws are tightened with a wrench. Since the size of the heads of the hex screws varies, a wrench set or an adjustable wrench is required for driving these screws.
- Phillips Screw: These type of screws provide a larger mating surface between the screw and the screwdriver which in turn minimizes wear. This also helps prevent slipping.
- Square Screw: These screw heads have a square indentation which minimizes slipping. A special type of screw driver is used for tightening and loosening.
- Torx Screw: Torx screws have six-pointed recessions. They provide more surface area for driving. They are tamper resistant and require the less-common torx screwdrivers.
- One Way Screw: One-way screw is similar to a slotted screw. It is tightened with a standard screwdriver. But this type of screw is tamper-resistant because special tools are required for removal.
Head Shape of screws:
- Pan Head: This is the standard head profile having an average diameter and an average height.
- Button Head: They have a curved top but similar to a pan head.
- Round Head: They have a more pronounced head compared to a button head.
- Flat Head: The screw heads having a flat top.
- Oval Head: Tapered underside with an oval top.
- Truss Head: These screw heads are large-diameter heads.
- Fillister Head: Thick profile head with a slight round top.
Thread Varieties of screws:
- Wood Screw: The threads of the wood screws are usually coarse and deep and are used in wood.
- Machine Screw: They have finer threads and are designed to be used in combination with a nut or tapped hole.
- Sheet Metal Screw: They have coarse threads designed to grab onto relatively thin sheet metal and are short in length.
- High-Low: They have two sets of threads with alternating heights. They are used for certain plastics and other low-density materials.
- Self-Tapping: Self-tapping screws have threads designed to tap their own holes.