As the name implies these types of screws are generally used in attaching wood to wood, although they are also used in some instances for attaching hinges handles and locks to wood. Also they are sometimes used in plastic type wallplugs for attaching an item to brickwork such as brackets and shelving etc.
Woodscrews afford a better grip in wood than smooth type nails or staples.
As the screws are tightened the thread has a tendency to draw the mating parts together giving a greater clamping force than that of smooth nailing.
The screws can also be driven and removed for adjustment without causing damage to the surrounding work area.
Common head styles are Countersunk Slotted, Round Head Slotted and Raised Head Slotted. These head styles are also available with a Pozidrive cross recess.
As well as the conventional part threaded woodscrews some types are now available fully threaded commonly referred to as chipboard type woodscrews. Chipboards are available in Pozidrive cross recess and the increasingly popular 6 lobe TX drive.
Also a Hexagon headed version is available commonly referred to as a Hex Coach Screw or Lag Screw.
In most cases a pilot hole should be used to avoid splitting some woods, also using screws in the end grain will greatly reduce the holding power so this type of usage is not really recommended.