This mini bulk pack provides 9 of the popular Estes A8-3 model rocket engines. These are used to provide low altitude flights for model rockets weighing roughly between 0.8 and 2 ounces which is typical of most rockets being 10 to 18 inches 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.