I recommend this article for some interesting insight into why industrial (ie. all-grades) trade unionism is more effective than craft (single-grade) trade unionism.

It was written by Irish Marxist James Connolly, who was a trade union organiser in the USA at the time (1910) that he wrote this article.

In it, Connolly writes that, "Industrialism is more than a method of organization – it is a science of fighting", and that, "The most dispersive and isolating force at work in the labour movement today is craft unionism, the most cohesive and unifying force, industrial unionism.

Obviously, he wrote 100 years and thousands of miles away, so the situation he describes is not exactly comparable to today. In those hundred years, many craft unions in both the USA and Britain have merged with others to form all-grade, industrial unions. But not in every industry - the rail industry in this country being a case in point.