Estes B6-0/B6-6 Engine Bulk Pack for Two-Stage Model Rockets - Includes 24 Engines with Starters, Plugs, and Recovery Wadding (1784)PLEASE NOTE: These are 18mm diameter engines designed for two stage rockets. Please refer to the instructions that came with your rocket (or the rocket's product description) to determine engine compatibility. Estes B6 0 B6 6 bulk pack includes 24 engines (12 of each engine), 30 starters, 24 starter plugs, and ~72 squares of recovery wadding all the rocket engine supplies you need to launch 12 *two stage* rockets! The B6 0 is a booster stage engine