Cattle panel sizes:
42 oustide diametre, 2mm wall thickness, HDG Pipe 1800H x 2100 (35KG) 
40 x 40 x 1.6 Gal RHS 1800H x 2100W (32KG)
40 x 40 x 2 Gal RHS 1800H x 2200W (41KG)