There are two types of letter openers: chadders and slitters.

Chadders use cutting wheels to slice off 1/8th of an inch from the top of an envelope. These models tend to be fairly inexpensive, but run the risk of damaging the contents of an envelope.

Slitters work by cutting through the top seam of the envelope. Because this process is more complex than that used by chadders, slitters tend to be less common. While slitters are unlikely to damage mail, they command a $1,000 to $2,000 premium over equivalent chadder designs.