The quad-butted Valite tubing was a seamed tubeset made for Fuji by Ishiwata. Ishiwata marketed it as EXO-V. It was a manganese-moly steel alloy (similar to R531, if I remember right), and many consider it to be the first "decent" tubeset to come out of Japan at a price sustainable by the mass market.

Here is a link to an old Ishiwata catalog shot showing the tube specs:

http://www.equusbicycle.com/bike/ishiwata/page-02.jpg

Because the tubing was seamed, Ishiwata could (more or less) contour the wall thickness any way they wanted to. They could put it lots of different butts, with nice tapered transitions between the different wall thickness sections to minimize stress risers. Once they tooled up, they could just roll out the steel in sheets with the right thickness profiles, bend the sheet over a mandrel, and weld them together at the seam.

'Course, seamed tubing has its drawbacks relative to seamless tubing, but I've never seen a tube come apart at a seam, even after catastrophic crashes that buckled the top and down tubes. Seamed tubing is a bit heavier, but (I hear) it's a bit stiffer as well.

My Two Cents,