The function of this product converts the thread size of your lens to the thread size of any other accessory (such as filters, hoods, flashes and lens converters). It easily screws onto the front of lens of the same thread. This product have multiple of features. Some of the features are brand new, high quality, solid, lightweight, great tightness, and no wobbling or cross-threading. This product is environmentally friendly material made of aircraft grade magnesium. It has a superfine frame polished with strict surface treatment. The purpose of this product is to fits any lens with the same filter thread; manual or autofocus, digital or film. To order your product here is some guide: the first number is always the lens thread size, the second number is the filter size of the accessory. If the first number is bigger, it's a step-down ring.