End cap for Ikea KVARTAL triple track curtain rail

This is a replacement end cap for an Ikea KVARTAL triple track curtain rail. The original (in ABS, shown in the background) breaks easily. The design here should be significantly stronger and sturdier, even when printed in PLA. I assume printed ABS will be stronger still. For strength, print with thick walls and close to 100% infill. The screw hole threads needs to be finished with an M4 threading tap. Use the original M4 set screw. See http://www.ikea.com/us/en/catalog/products/80079363/