Carbon Fiber Solid Rod 6mm 8mm 10mm 12mm 14mm 15mm 16mm 18mm 20mm x L500mm. Be aware that measurement in Millimiters. Allow Outer diameter tolerances around +/-0.1. To Calculate the inside diameter of the tube, please remember that you must multiply the wall thickness by two and deduct it from outer diameter. For example, OD10m with wall thickness 1mm, so the inner diameter is 8mm.