It is an easy upgrade to the optical finders that are usually found on 4.5" and 6" reflectors and many refractors as it is a straight replacement, using the same two protruding studs. The holes on the base of the finder are slotted so that they will fit from 21mm to 26mm across. Specification Material: Metal + Plastic Color: Black Net Weight: 72g/2.52oz Package Includes: 1 x Red Dot Finder Scope 1 x Mounting Bracket Base