Final answer:
The ideal needle for sewing extensions onto a track should be small and thin to ensure accurate and clean stitching.
Step-by-step explanation:
The blunt, custom-designed needle used when sewing the extension onto a track should be small and thin. The reason for this is that a small and thin needle allows for greater precision when sewing the extension onto the track. It can easily navigate through the fabric and create smaller, less noticeable stitches.
In contrast, a large and thick needle may leave large and visible holes in the track and may not provide the level of detail and precision needed for sewing extensions. A medium-sized and sharp needle could be too aggressive and could damage the track or fabric.
Overall, the ideal needle for sewing extensions onto a track should be small and thin to ensure accurate and clean stitching.