Estes A8-3 Model Rocket Engine Pack - Includes 3 Engines with Starters & Plugs (1598)PLEASE NOTE: These are 18mm diameter engines. Please refer to the instructions that came with your rocket (or the rocket's product description) to determine engine compatibility. Estes A8 3 engine pack includes 3 engines, 4 starters, and 4 starter plugs The A8 3 is a single stage engine designed for model rocket flights weighing less than 3 ounces, including the engine. This engine is ideal for smaller fields, or to be able to see the entire flight