Breaker-grozier pliers are tools used by Glaziers to break and finish glass in a controlled manner. They are dual purpose pliers, with a flat jaw that's used for breaking out scores and a curved jaw that's used for grozing flares from the edge of broken glass. Both jaws are serrated for removing flares and tiny points of glass.
To break out a score, the glass to be removed is held firmly in the pliers, with the flat jaw on top of the glass near the score line. A sharp bend downward breaks the glass at the score.
To remove unwanted glass flares and unwanted points , the glass piece is held with one hand with the pliers curved side up. A gentle upward rolling scrapes the glass edge (grozz) against the serrated teeth removes unwanted glass flares. This removal of grozz is known as grozing.
You can also use the tips of these pliers, in a chewing motion, to remove small sections of glass or nibble out deep inside curves.
Breaker/grozier pliers are a combination tool. Glaziers also use single-purpose pliers such as breaking pliers, with two flat jaws, and running pliers, which apply even pressure on both sides of a score to make a controlled gentle break on the glass.