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All About Screws

11/7/2012 6:04:58 PM | by Anonymous


Screws are threaded rod with a head on one end and tapered and pointed on the other. They are driven in a helical movement to a wood or metal as a fastener to join parts. The thread design allows it not to come out easily as compared to nails but screws are easier to remove when applied with external force. Screws are driven by using a screwdriver that tip fits the head of the screw. There are numerous types of screws and a matching screwdriver is made as a response to the former. Bolts are commonly mistaken as a screw because of their similarities in design. Their differences can be distinguished on how they are installed. The head is turned when being inserted while the nut is turned to tighten the grip of bolts. Bolts are always untapered while screws, though often tapered, can also be untapered.


Features of Screws

Screws come in various lengths and gauges (diameters) and made from different materials depending on their applications. The effectiveness of the screw can be determined on its length. It should be long enough to go all throughout the object to be fastened and still able to be deeply inserted on the surface where the object will be attached to. The length of the screw is measured from different points depending on the head type. Despite of the fact that screws are produced with different diameters, or also called gauge numbers, only two types are being used in most jobs. The 50 mm long gauge 8 is thick enough for almost any types of applications especially in do it yourself (DIY) jobs. The other one is gauge 10 which screws for up to 75 mm long and is applicable for heavier-duty fixings. The longer and higher the gauge of the screw, the more holding power it has. Beside the gauge and length, other factors being considered to make sure that the screw will match its application are the strength, usability and corrosion resistant properties.


Screw Head Types and Uses

There is almost a designated screwdriver for every type of screw head. Two of the types that we might be most familiar with are slotted head and cross head screws. For slotted head, normal flat blade screwdrivers are used. Crosshead screws include Philips and pozidrive head screws. Unlike Philips screws where only Philips screwdriver can be used, both Philips and pozidrive screwdrivers can fit in to pozidrive screws. The advantage of crosshead screw is that it allows more power to be driven by the screwdriver even though Philips screwdrivers are originally designed to cause the bit to cam out at a certain point to prevent over-tightening. Pozidrive is an alteration to the Philips which was built to further reduce the slipping of screwdrivers. Another type of screw head is Robertson drive or more recognizable as square drive because of its square hole on the head. It is designed to maximize torque transferred to the driver making it the type that has the least chances to slip out.

Countersunk screw is a slotted head screw which is used on applications where the head must be tightened flush to the surface. This is mostly applied on general woodworking such as fitting hinges to doors.

Round head screw has a slotted head used for joining parts together and on materials that are too thin to be countersunk. It can be decorative especially if made out of brass.

Raised head screw is a combination of countersunk and round head screw. It is used when aiming a neat finish on the object.

Crosshead screws namely Philips and Pozidrive screws are applicable when attaching screws in narrow areas or corners.

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