AP Pony-cylinder Cambands are an extremely neat and secure method of mounting 2 or 3 litre pony cylinders alongside your main cylinder. The pony band can either be used as a replacement for the standard AP BCD camband by threading the pony bands through the camband slots of any AP BCD backpack (fits pre and post 2007 BCD ranges) or alternatively, it can be simply cammed directly onto any main cylinder as shown. Available in 4 sizes: BK18 - 4\"/102mm diam Pony to a 7\"/178mm diam main cylinder BK19 - 4\"/102mm diam Pony to a 8\"/203mm diam main cylinder BK20 - 4.5\"/114mm diam Pony to a 7\"/178mm diam main cylinder BK21 - 4.5\"/114mm diam Pony to a 8\"/203mm diam main cylinder It is advisable you measure your cylinders but typically:   10 and 12 litre cylinders = 7\" diam 12 litre dumpy and 15 litre cylinders = 8\" diam 3 litre steel cylinders = 4\" diam  3 litre aluminium cylinders = 4.5\" diam  2 litre steel cylinders = 4\" diam  2 litre aluminium cylinders = 4.5\" diam  1.5 litre aluminium cylinders = 4.5\" diam