"Standard" 1-1/8" head tubes are indeed 34 mm and that's the most common size. The "EC" designation means a "External Cup" or the common press-in style of upper and lower cups and require a 30 mm crown race diameter

However, 1-1/8" headsets are also made to fit a variety of headtube diameters from 34 to 52 mm in EC press-in styles, ZS zero stack styles and IS integrated types. Also, there are types for straight 1-1/8" steerers (30 mm crown race) and 1-1/8"x1-1/2" tapered steerers (40 mm crown race).

A visit to Cane Creek's web site and a review of their series 40 headsets and their tutorials will show you the range of styles and sizes. There are a lot of options so be sure to order the right size and type.