What are Screws ?
screw is a type of fastener, sometimes similar to a bolt (see Differentiation between bolt and screw below), typically made of metal, and characterized by a helicalridge, known as a male thread (external thread) or just thread. A screw is an inclined plane wrapped around a nail. Some screw threads are designed to mate with a complementary thread, known as a female thread (internal thread), often in the form of a nut or an object that has the internal thread formed into it. Other screw threads are designed to cut a helical groove in a softer material as the screw is inserted. The most common uses of screws are to hold objects together and to position objects.

There are vairous types of Screws viz :

Machine ScrewsSheet Metal ScrewsFlat Head MS & SMS ScrewsOval Head & Binding Head ScrewsHex Head & Hex Washer Screws
Round Head & Pan Head ScrewsTruss Head & Fillister Head ScrewsDeck ScrewDrywall ScrewsThread Cutting & Rolling Screws
Phillips, Slotted & Socket ScrewsSix Lobe, Square & Security ScrewsSet ScrewsSocket ScrewsSocket Cap Screws
Slotted Flat Head Cap ScrewsSelf Drilling ScrewParticle Board ScrewWood ScrewSems Screw
Self Tapping ScrewConcrete ScrewChipboard ScrewEuro ScrewStainless Steel Screw
Thread Rolling ScrewRoofing ScrewConstruction ScrewsCollated ScrewWing Screws
Thread Cutting ScrewCoach screwsFurniture Screw Cap ScrewsMachine screwsSheet Metal Screws
Lag ScrewsBinding Post ScrewMultiple Material screwsWind ScrewsDrive Screws
Eye ScrewsWeld ScrewsFlooring ScrewsDowel ScrewsRoofing Screws
Accordion ScrewsEuro ScrewsJack ScrewsThumb ScrewsScrew Hooks
Screw EyesSecurity Screws