Newbie Bike builder

[Jake]

Just sitting here wasting time at work thinking of a bike design and sketching it out...a couple of questions.
1. What is the diameter of a standard head tube?
2. Is it possible to use 2 inch diameter tubing for the top tube and the down tube when using a standard head tube?

 

[deorman]

Older bikes w/common caged bearings are 1 14" inner diameter. You could squeeze down or cap the end of an oversize tube.