There is a magnet at the bottom, which can be adsorbed on the top or bottom of iron items, making the measurement more accurate and, Perfect for woodworking projects, furniture installation The spirits bubble sets contains 4 different types of levels: pocket, t, string line & circulars The T Bubble is, and provides for front-to-back or side-to-side leveling, with 2 optional screw holes for permanent mounting or apply adhesive for mounting The String Line is, lightweight, and resistant to wear With moulded hooks to enable the to be hung from a builder line.This bubble is accurate, and lightweight, it can be used for leveling the position of telescopes, tripods, cameras This bubble comes with a compact box, which can easily store these small tools and is very to carry, Manufacturer: TFAOYS