A bicycle stem is a small part carrying an enormous responsibility. It clamps the steerer tube at one end and the handlebar at the other, translating every steering input and swallowing every impact through two bolted joints and a short aluminium bridge. Taking one from idea to finished component passes through five disciplines, and each stage rewrites the design that came before it. CAD defines intent. Reach, rise, stack height, clamp diameter and bolt circle are all locked in parametrically, so a change to bar diameter ripples through the whole model rather than forcing a redraw. The faceplate split, the fillet radii and the wall thickness beneath the steerer clamp are decided here, and they largely determine whether the part survives later. Simulation interrogates that intent. Finite element analysis applies the standard load cases, including forward bending, lateral bending and torsional loading at the bar clamp, and reveals where stress concentrates. Fillets that looked generous...