The MK2 base version is designed for 6" Clear PVC = https://www.amazon.com/dp/B09NJLNW58?psc=1&ref=ppx_yo2ov_dt_b_product_details
Tube dimensions I measured:
Wall thickness: 3,01 mm
OD: 151,822 mm
ID: 145,800 mm
Patreon member purchased his tubes at Woodcraft:
https://www.woodcraft.com/products/woodriver-dust-connection-clear-pvc-tube-36-x-6
Free Shipping with Code "PENCIL" $20 each
Check your tube dimensions always with the scaling ring.