This study focuses on improving the quality of intravenous catheter (IVC) production by solving the issue of side contour tolerance (SCT) at the capillary tip. The main problem found in the production line was a high rejection rate, especially for catheter sizes 24G and 20G, due to the capillary tip diameter being smaller than the lower specification limit. This defect leads to non-compliance with product standards, affecting the safety and performance of the catheter, and increasing waste and production delays. The variation was suspected to be caused by wear in the die used during the tipping process. The objectives of this study are to measure the SCT accurately, identify the root cause of the variation, and suggest improvements to reduce the defect rate. Measurements were taken 1 mm from the capillary tip using a smart microscope, and the data were analyzed to check whether they met the required specification. A root cause analysis using a fishbone diagram was done and identified die wear as the main cause of the capillary diameter shrinking over time. To find the best machine setting that can reduce die wear and improve SCT control, a factorial design of experiment (DOE) was conducted. Two factors were studied: die orientation (2 levels) and punching force (5 levels). The experiment aimed to see how these settings affect the capillary size and to determine the best setup to reduce variation. The results showed that both factors have a strong impact on SCT, and that using a horizontal die orientation with lower punching force helped produce better capillary dimensions. In conclusion, this study shows that identifying the root cause of variation and optimizing machine setup can reduce the rejection rate, improve capillary quality, and enhance the overall production process of intravenous catheters.