Adapts D engine mounts to hold a standard engine.Two simple steps transform a standard engine into a D size. Insert a standard engine into the adapter, and insert the adapter into a rocket. 3 adapters per pack. Reusable.NOTE: This motor adapter has been tested in products that use ESTES metal engine hooks. It may not work with other brands of engine hooks.Rockets weighing up to 4 ounces that would normally fly on C11 or D12 engines can be flown on B and C engines.