Join Date: May 2011
Location: Upstate NY
Bikes: Bianchi San Mateo and a few others
What dimensions do you need that you can't measure? You just need to know its length and diameter. Diameter should be easy enough to figure out. If the frame is roughly the age you think it is, or even within a few decades, I'd assume it was designed for a fork with a 1" steerer tube, so you just need to measure its length to choose an appropriate fork. The fork's steerer tube will need to be longer than the frame's head tube by enough length to accommodate the stack height of your headset. If the fork's steerer tube is too long, it can be cut to fit. The steerer tube's unthreaded portion needs to be shorter than the frame's head tube. In other words, when the fork is inserted, all of the steerer tube that protrudes from the top of the head tube must be threaded.