Sparklet type CO2 cylinders, packed in boxes of 10. Each cylinder contains 8gm of CO2 and needs to be screwed onto an appropriate pin valve using a bulb holder (not supplied with the refill boxes). They will not work with standard S30 valves as they need to have a pin present as part of the valve to pierce the bulb.
They should only be used to replenish gas pressure in a barrel once the natural pressure produced during secondary fermantation has been exhausted. If you try and add gass whilst there is still pressure in the barrel, the pressure release vent rubber will operate and let all your CO2 out. If you are trying to shortcut the serving time by avoiding secondary fermentation and immediately adding serving gas via these bulbs, you will find that you will end up using several boxes to dispense your beer.
Whilst CO2 and N2O are completely safe, when they are compressed into cylinders they fall foul of the "Hazardous Goods" regulations and cannot be shipped via the Royal Mail. If you have any CO2 or N2O cylinders in your order, you MUST choose the Courier delivery option.