“i” means series, generally refers to small size. For example, I3E, I5T. “S”means small upgrade. “EOS ”means Goddess, and generally means a tiny flashlight, similar to Odin.“ T ”generally refers to the button with the tail
not sure about the i but i know that i3t runs on a AAA batery and the i5t runs on a AA thr higher the number the bigger the batery and the i5r is the rechargeable version of the i5t hence the ''R'' for rechargeable.