This is the primary tool for inspecting the neck area of all cylinders. Set of two inspection mirrors, size 0 and 1, 2x magnification with extension handle for inspecting inside cylinders. Diameters are 1cm and 1.5 cm so they easily fit into even small cylinders. The 2x magnification with the extension handle makes an excellent tool for inspecting the neck and threads of most cylinders. The magnification helps locate concerns and the sizes are compatible with most cylinders.