Coach screws can also be known as lag bolts or lag screws. They are a type of heavy duty fastener for fastening metal pieces with timber and also to fasten heavy timbers. With a hexagonal head the screws require a wrench or socket spanner to be tightened or unscrewed. Coach screws can be used with wall plugs to anchor heavy objects, such as a TV arm or satellite dish, into masonry or concrete. They are also used in heavier installations and for fixing timber to masonry.