What is chuck size?
When selecting a cordless drill driver, you will probably come across the term ‘chuck size’. This refers to the maximum shank diameter the chuck will accept.
The shank diameter of a bit is the measurement across the centre of the shank. Hexagonal shanks are always measured across their flats.
The measurement for a straight shank's diameter can be take from any point around the circumference.
What size chuck do I need?
Cordless drill driver chucks come in the following sizes:
10mm (3/8 inch)
13mm (1/2 inch)
Quite simply, the larger your chuck size, the larger shank diameter it will accept.
Generally, if you want to drill holes larger than 20mm in diameter or drill into materials such as metal, then consider purchasing a drill driver with a 13mm chuck, to accommodate larger bits.