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Anchor screw – Acts as an anchor for wire or suture.Position screw – Holds two fragments in position without compression.Reduction screw – To reduce displaced fracture by pushing or pulling.Lag screws – For inter-fragmentary compression.Neutralisation screws – neutralises forces on the plate in plate fixation.Designed to have better purchase in the cancellous bone.Thread diameter to core diameter ratio is more.Designed to have better purchase in the cortical bone.Thread diameter to core diameter ratio is less.Orthopaedics screws may be classified depending on the following characteristics. Phillips and Woodrugg screw heads made slippage at the driver–head interface a rare event.Titanium alloys introduced in the 1970s.In the same year, Bagby and Janes, designed “impacting” bone plate with low profile and oval holes that permitted eccentric screw placement.In 1958, Maurice Müller and other Swiss surgeons formed the AO/ASIF (Arbeitsgemeinschaft für Osteosynthesefragen/Association for the Study of Internal Fixation) to study the bone healing and the effect of internal fixation.Buttress thread design instead of V-shaped thread to increase pull out strength.Reduction of thread surface area to one-sixth that of machine screws.Alteration of thread diameter to core diameter from 4:3 in machine screws to 3:2.He advocated 3 key modifications in the machine screws to make them suitable for bone fixation. Robert Danis designed the compression plate.He designed the Sherman plate with round holes, which was the gold standard until the AO design was introduced. Sherman in 1912 published his recommendations on the essential properties of bone screws. Use of screws for fixation was started almost a thousand years later due to technical difficulties in their manufacture.Archimedes is thought to have invented the screw in the third century BC.Newer locking plates do not depend on the friction between the plate-bone interface it acts as an internal fixator by using locking of screw head into the reciprocal threads of the plate to form a fixed angle construct.In conventional plates they act by increasing the friction between the plate and the bone. Screws can be used for attachment of implants to bone, bone to bone fixation or for soft tissue fixation or anchorage.Thread design should maximise initial contact, enhance surface area, dissipate and distribute stresses at the screw-bone interface and increase the pullout strength.The primary functional objective in the design of a screw is to dissipate and distribute the mechanical load. It converts torsional forces into compression. Screw is a cylinder with spiral threads running on its outer surface.Rajesh Purushothaman, Associate Professor, Medical College, Kozhikode, India