Since pipe shape and design can vary allot...I like to use the first baffle as my reference point because it's what really matters...As Bill mentioned the music wire method comes in very handy to "find" the first baffle if there is no weld for reference...

In the first photo below you'll see a Hatori 650 pipe and the first weld is the first baffle...

The Bolly pipes I have..The location of the first baffle is not consistent...So measuring is a must...

The other photo below shows a few different models of Hatori pipes...The 601, 650 and 700...You can sorta tell the difference in the spacing and placement of the baffle welds...The 601 is a 10cc Tuned Pipe/muffler, the 650 is 10cc (Long Chamber) and the 700 is 10cc (Super Long)...

Apparently at some point Hatori changed the "Look" of the pipes from the smooth style like airbusdrvr's to the type like mine (welds showing)...Dunno when that happened?? I have a 1987 Hatori catalog which shows the "smooth style" pipes...I forget exactly when I bought my first one..but it seems like it was the early 90's...