This ROM pop pin has a yellow knob and fits some models of strength by Matrix. 

Pop pin fits some Aura G3 models, some G2 single station models, and some Varsity strength. 

The pop pin serves different functions based on the machine it is found. 

ROM is the range of motion and that is the purpose of this pin on machines. It allows you to adjust the position for the range of motion.

The thread type of the pin is 3/4" x 10 TPI.