UKELELE STRING SET D'Addario EJ87C Titanium Ukulele Concert string set for ukulele. Optimized for standard GCEA tuned concert ukuleles. Caliber: Titanium .025, .033, .040, .029. D'Addario Titanium Ukulele strings are made from a dense monofilament material that has an attractive translucent purple hue and a smooth, polished feel similar to nylon. This unique material is particularly beneficial to the ukulele, due to its slightly brighter and more projected tone, resulting in more volume, clarity and dynamics.