Barbells are a basic piece of gym equipment you really can't do without. There are two main sorts of bars: 1" and 50mm (Olympic) types. Bars with 50mm diameter collars are 'Olympic'. The simple rule here is that unless you are getting a 1" bar for free, spend the little extra and buy an Olympic bar. You will not regret it. An Olmypic sized bar can cost as little as £70 (or over £1000)
Better quality bars will come with a lifetime guarantee. We say, buy quality once.