The zip file contains all the lowercase letters written with the ROCKWELL font individually saved each as a .stl file plus a .stl file containing the entire alphabet.
The Alphabet.stl file containing the entire alphabet was created and printed with an Ender3, it can happen that, for the Delta printers, the image is too big, in this case the dimensions can be scaled. Created with Fusion 360 Printed with Creality Ender 3
Have fun and good 3D printing!!!!