Sorry it took so long... I wanted to remeasure them before answering to be sure you get good info...
I measured the large diameter "main" pipes in several locations and on both sides. They read between 1.115" and 1.128", which is roughly 28.5mm, so I'm gonna go with 1 1/8". (This includes the powder coating, so maybe they were 28mm pipes? If that is a standard pipe size in Japan...?)
The little "accessory light roll cage" pipes measured between 0.850 and 0.870", which just doesn't seem to line up with any "standard" size. However, these little pipes are almost 100% curved and there wasn't much space to measure a straight, unbent, and unwelded section.
This was on my 2014 DL1000 Adventure... I assume they are the same for other years.
Last edited by Grimmer; 06-24-2019 at 08:25 PM.
Reason: Added motorcycle model reference.