What is an expansive bit?

An expansive bit is a tool for boring holes of variable width.

Expansive bits are made with adjustable cutters that can be extended or retracted. They were designed to eliminate the need for DIYers to buy sets of drill bits.

They can be used on all types of wood, as well as other relatively soft materials such as plastic and plasterboard.

As expansive bits are becoming outdated thanks to the falling costs for sets of other types of wood bit, they are starting to be considered specialist tools, despite their versatility. 

Thanks to the adjustable cutter that forms the functional part of the tool, expansive bits are also known as 'adjustable bits'.