The 9809-K Classic Corner Mirror Mount centers a 1.0 inch (25.4 mm) diameter optic at the fourth corner of the square formed with the three adjustment screws, allowing you to get tilt without translation, and pure translation all in a single mount. For pure translation, simply turn on Allen-keys the same amount. A 1° error in one Allen-key results in only 0.0012° tilt in the face plate. For tilt without translation, use two Allen-keys, or for applications when translation is less important, adjust the tilt with just one Allen-key. The proprietary, precision, Hex-key actuated 1/4-80 screws give you increased durability, better repeatability, and even more precise adjustment than comparably priced mounts. Because the optic sits close to the edge of this mount, it is ideal for applications where clearance is an issue.