This is an original 1st generation 2 piece actuator for the Colt 1928 Navy model Thompson. Designed by Oscar Payne in 1927 to satisfy a requirement from the US Marines to reduce the rate of fire of the Model 1921 Thompson. This 2 piece heavier actuator in addition to a smaller, stiffer recoil spring and buffer assembly reduced to rate of fire from 800 rounds per minute to 600 rounds per minute. All original and in excellent condition.