Gosky Precise Metal Bahtinov Focusing Mask for Telescopes Dew Shield or Front End Diameter From 83mm to 116mm 3.5"- 4.5"  for More Precise and Faster Focusing The Bahtinov Mask Made of aircraft aluminum, not plastic. And it has whole anodizing aluminium process. Masks now feature 4 holes which can be attached with 4 screws to prevent the mask from falling all the way to the ground The Bahtinov Mask makes it perfect to focus of your CCD, DSLR or Webcam in seconds. Light weight so you wont upset the balance on your scope. Suitable for telescopes front end diameter 83mm to 116mm 3.5"- 4.5"  , Universal adaptation, 4 bolts with plastic cover allow the mask to be simply attached to any telescope