Classifiers are designed to classify material to a specific size and screen out large rocks, gravel and debris. They fit on top of 5 gallon buckets and most gold pans. When the material is screened to the same size it makes panning material much easier. They can be used dry or wet. Most finishing equipment has a recommended mesh size in which material should be screened to for optimum gold recovery. Classifiers are a must for Gold Prospectors,Treasure Hunters and Rock Seekers. These classifiers are made of ABS plastic and stainless steel screens. They come in nine different sizes. The mesh/screen size refers to the size of the classification achieved. Examples: A 1/2 inch mesh/screen has about 8 openings/holes per square inch, A #8 or 1/4 inch has about 16 openings/holes per square inch. A#12 or 1/2 inch has about 32 openings/holes per square inch and so forth.