These hardeners are meant to be used with Pro Glas 1200 resin- Part A. The mix ratio is 2 parts resin to 1 part hardener. It comes in three speeds- fast, medium and slow. This resin is used in many applications including hand layup, laminating, marine construction, tooling, epoxy face coats, kit aircraft and vacuum bagging. It has low odor and low to moderate toxicity.