Estes B6-2 Model Rocket Engine Pack - Includes 3 Engines with Starters & Plugs (1605)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 B6 2 engine pack includes 3 engines, 4 starters, and 4 starter plugs The B6 2 is a single stage engine designed for model rocket flights weighing less than 4. 5 ounces, including the engine Recommended for use with the Tazz, Sidekick, Double Ringer, Der Red Max, or