steel frame tube dimensions remained constant for decades
during the early to mid 20th century; 25.4mm top tubes and steerers,
28.6mm seat and down tubes, and 31.75 head tubes.
in the late 70s, owing to the advent of trickle down from the
nascent mtb industry as well as the need to change for 'the sake
of it', shapes began to grow larger while materials eventually
improved in quality. joining processes also evolved and, ultimately,
convention went out the window. to wit, any size different from those
above are considered 'oversize'. fwiw, 'oversize' has been
size for almost 20 years.

as the industry (might) have you believe, "if we keep improving
the quality of these bicycles, they will, one day, go by themselves."
ironically, despite all the changes offered up and consumed, it
is still an even playing field, with the rider being the most
important component.

for builders still using lugs for joining, the modern steels offer
a wonderful menu from which to choose pipes to make a strong,
light, and responsive frame AND FORK without depending on
dated, out-of-production materials and/or techniques.