Anodic oxidation, it is durable and rustproof. High hardness, rustproof, non-corrosive, permanent use. Perfect 90° Corners: This precise clamping square is designed to be clamped on boxes, frames, etc. to help you square during gluing. This right angle positioner has two extra notches. True right angle for inside and outside squares. Base and folded for straight and parallel. How to Use: Place a square in the corner of the two pieces you need to square and secure with a set of clamps. Metric and inch graduations. Accurate calibration, easy operation, will not easily damage fragile cutting edges. Available in 12 cm, and supplied in a pack of two. Professional Design: Designed to be attached to boxes, picture frames, shelf cabinets and for outside corners, etc., to help with squaring when gluing. Beveled edges, easy to handle and will not damage fragile cutting edges. Wide Application: You will have exactly what you need to perfectly create boxes, drawers, cabinets, frames, furniture,