Reamers are end-finishing cutters useful for finishing a previously cut hole to an exact size. Most people use reamers for cutting metal. To efficiently cut holes to size, reamer blades are made from high speed steel and carbide. The adjustable reamers can be set to different sizes within a few centimetres. They work well for holes for which standard-sized reamers aren't appropriate. Setting an adjustable reamer is easy to do as reamers are meant to be adjusted and secured by hand.
Twist the top nut clockwise along the metal rod of the reamer until you get to the desired size for the reamer.
Slide all of the blades up to meet the top nut. They should be easy to push up by hand.
Twist the bottom nut clockwise up to secure the bottom of the blades against the top nut.
Don't turn the nuts too tightly against the blades of the reamer.