The sword breaker was a Medieval English dagger, a quillon dagger which was fitted with a relatively simple guard (hilt) but had a massive saw-edged back spine. The purpose of this dagger was to catch an opponent’s sword blade with the saw-like teeth.
The sword breaker dagger was often used in the left hand to parry and catch opposing sword blades. A quick twist of the wrist could sometimes break the enemy's sword.
Average total length was 16" - 18" long with the blade being 10" - 12" long. Blade was usually 2" wide from back spine to edge. Approximate weight was 1-1/2 to 2 pounds.