This level is made from high strength aluminuim alloy with black matte anodized finish. Each bubble is fixed in place and calibrated to the body assembly individually. Will fit all picatinny style rails and can be installed or removed with out removing the scope, requires less than 1/8 inch of space from bottom of the scope tube to the top of the rail. We have replacement bubbles, should you break the vial send it in and we will install and calibrate for $25.00. A must for scope installation to level the rifle.