Product Highlights With a 30mm maintube, edge-to-edge optical sharpness and excellent low-light capability, the Mark 4 16x40mm LR/T M1 is not only astoundingly durable, it is optically outstanding as well. The M1's oversized adjustment knobs give the user audible and tactile confirmation of each 1/4-MOA click, and can be zeroed after sighting in.