Estes 3 Packs of D12-3 Model Rocket Engines - Total of 6 Engines with Starters & Plugs (1566PK3)PLEASE NOTE: These are large (24mm diameter) engines that will only fit certain model rockets. Please refer to the instructions that came with your rocket (or the rocket's product description) to determine engine compatibility. 3 Packs of Estes D12 3 engines total of 6 engines (each pack includes 2 engines, 2 starters, and 4 starter plugs) The D12 3 is a single stage engine designed for rockets with a maximum lift weight of less than 14 ounces