Yes, both T6 and T5 are M8 nuts in the knobs. Depending on the diameter of the frames you’re clamping you might get away with using the existing bar. From memory, the T6 clamps are about 30mm deeper than the T5 clamps. I wanted to be able to fully open the clamp so swapped the bar. It’s quite straightforward following the steps below:
– Undo and remove the knob.
– Slide the old clamp and external sleeve off the bar.
– push the bar out through the top of the bracket which attaches to the top rail of the rack. Be careful that the two plastic pieces that fit round the top rail don’t fall out.
– Remove the nut from the end of the bar and swap over to the new length of threaded bar. It’s worth adding some locktite to this nut to stop it unthreading when you’re trying to undo one of the knobs.
– Go through the stages above in reverse to put it back together.
Hope that helps