A steel tank is used most commonly in NL/BE. They come in 200 and 300 Bar tanks. An Aluminium tank is lighter than a steel tank. However can only hold 200 Bar. The carbon tanks are even lighter than the aluminium ones, however, are only available in 300 bar.
200 bar tanks can be filled up to 200 bar and sometimes even up to 232 bar. 300 bar tanks require a special DIN valve, and you will need a DIN300bar connection on 1st stage for the regulator set.
A single tank consists of 1 tank cylinder and a valve. Depending on the type of tank it may come with a mesh netting and/or tank boot. A double set consists of 2 tanks, 2 lateral valves, a bridge and metal bands to stabalise the set. When we talk about a cylinder, it is just the cylinder without any valve.
Weight of the cylinder without any valves, tank booties etc. The weight may vary a couple of ounced per cylinder.
Diameter of the cylinder
Height of the cylinder - without tank boot etc. The height of a standard valve is approximately 6,2 cm.