1Applicable door thickness is 55-90mm, suitable for wood, fiberglass or metal door. Easy to install, the door viewer can be replaced within 5 minutes without tools. 2Precise thread casting, easy to install, the length can be adjusted properly, anti twisting, anti-skid and anti-pry, protect your home from burglary and home invasion. 3The 220-degree viewing angle provides security for identifying visitors from behind the locked door, and you can easily view the entire surrounding area of people standing outside. 4The inner wall is finely butted with thread, safe and without danger, which can effectively prevent thieves from prying and destroying door viewer with tools, more convenient to use. 5A sturdy and heavy duty viewer cover increases your safety. After cover the cover, visitors outside cannot see through the viewer into your home, providing protection for your safety.