This mini bulk pack provides 9 of the most popular model rocket engine in the market. The Estes B6-4 is used to provide medium altitude flights for model rockets weighing roughly between 1 and 2.5 ounces which is typical of most rockets being 1 to 2 feet tall. Refer to the instructions or packaging that came with your model rocket for the engines you should be using. Estes model rocket engines are the standard in the model rocket industry for easy to use and reliable propulsion for your model rockets.