The 3/4" Watts 007M1 double check assembly began production in 1991 and was replaced with the 007M2 1993. The "M" stands for modification. The 3/4" 007 went through three modifications for a total of four different models (007, 007M1, 007M2, 007M3). Repair parts do not interchange between models so be sure of your model before ordering repair parts. The 007 is an inline check design with a single access cover. The body is of bronze construction. Fully testable.