On Fibenare guitars we use extrahard nickel silver frets with 18% nickel content available in five different sizes (with NO extra charge), where dimensions are the follows:
Jumbo: 2.8mm wide 1.4mm tall
Medium: 2.5mm wide 1.2mm tall
Small: 2.1mm wide 1.1mm tall
Vintage Jumbo: 2.7mm wide 0.9mm tall
Tall & narrow: 2.3mm wide 1.4mm tall
Medium frets are available of non-allergic alloy & small frets are available of stainless steel material. These materials are available at extra charge.