below is a tube holding jig i made for bandsaw.
its made from offcut of 10mm plate left over from another project 2 antenna clamps, and some m8 studding.
first off i marked position of mounting holes in brackets onto the plate.
then i drilled and tapped plate m8.
then i bolted lower bracket down to plate.
for smaller tubing i use flat side of upper bracket for bigger sizes i flip it over.
can do 10mm to 40mm tubing on it only limited by length of studs i used.