Anodic oxidation, it is durable and rustproof. High hardness, rustproof, non-corrosive, permanent use. Perfect 90 corners: This precise clamping bracket is designed to be fixed on boxes, frames, etc. to help with squaring while gluing. This right angle positioner has two ex-tra notches. True right angle for inside and outside squares. Base and folded for straight and parallelism. How to: Place a square in the corner of the two pieces you need to square and secure with a set of pliers. Metric and inch graduations. Precise calibration, easy operation, will not easily damage fragile cutting edges. Available in 12cm, and comes in a set of two. Professional design: designed to attach to boxes, picture frames, shelf cabinets and for outside corners etc to help square when gluing. Beveled edges, easy to handle and won't damage fragile cutting edges. Wide Application: You'll have exactly what you need to perfectly create boxes, drawers, cabinets, picture frames, furniture, etc. Some woodworkers even find it useful to incorporate them into their jigs and fixtures. Satisfaction - Great utility - Square of efficiency.