The 15kg Butane bottle often used in the larger cabinet heaters. It fits the 21mm push on butane regulators. 

Note: This bottle is also good for use on BBQs though normally requires the BBQ regulator changing, we do hold these in stock or choose the option below (Great option whilst bottles are in short supply at the moment).  

Calor always have better stock levels of these 15kg bottles than the normally used 13kg patio.