IIRC, the M1 style cannot be covered with a cap. In other words the M1s are exposed. The target type has caps to cover them up. Also the M1 has heavier set screws. My turrets are pretty stiff to turn, so if they are all that way I don't think there's much chance of turning them by accident in the field. There are many others here much more knowledgeable than myself and I'm sure will chime in.