Explainer Hub on Instagram: "This video shows the ink-filling stage in pen manufacturing. Liquid ink is stored in temperature-controlled tanks to keep its thickness consistent. The ink is then pushed through narrow filling needles that inject a precise amount into each pen tube or cartridge. Accuracy is critical — too much ink causes leaks, and too little affects writing performance. As the pens move along the conveyor, sensors check fill levels before the tips and caps are assembled. The pens a