The ONA PRO Odor Block is a powerful alternative to ONA Odor Block and is ideal for small areas such as grow areas, closets, foyers, attics, cars, gym bags, boats, kitchens, garbage cans, cupboards or vents. Simply remove the cap, or punch several small holes in the cap and place in desired location. The ONA Block measures 3" x 3" and will fit in most places.