I've just started to build a single gear road bike. I was donated a 21" Raleigh Milk Race Special that has now been blasted and powder coated a nice shade of blue. I've got some nice Weinmann yellow wheels coming. I want to replace the headset with a new one and I'm concerned about the thread size. I'm also not sure how to size the headset. Is it 1" or 1 1/8". I am a novice at bike building despite being 51 years old. Has anyone else had any experience of rebuilding or modernising these bikes? Any help will be much appreciated!