Black lines, internally fitted gives minimal parallax errors machined internal radius High optical clarity material Single bubble; Scratch free These level vials are Perfect for adding to all stationary equipment that can be leveled, such as stoves, refrigerators, washing machines, milling equipment, refrigeration equipment, heat pumps, furnaces, air handlers, campers and any tool, device or object where level is important. Add one to many of your hand tools to know when you are working at level. These level vials are more than most level vials built into hand tools, they are made thicker and stronger., Manufacturer: Mcnhbdgg