If you google either 'Industrial metal services IMS' or
www.isg-steel.co.uk The 25x25x1.6mm box section may come up as 1x1inch 16 gauge ERW . The seamless tube may come up as 1in x 14gauge and 3/4in x 14gauge CDS. Me I just brought 20x3 and 25x3 ERW seamed tube as it was £7.50 for 6mtrs of ERW instead of £38 for 5mtrs seamless.