Différences between MIT magnum M1 and M1.3 interconnect

Hi from France.
I am very pleased with shotgun S1 interconnect and want to go to magnum rca. I don't t find M1.3 in Europ and buying in USA is very expensive as I shall have around 25% taxes. So my question do somebody knows the difference between MIT M1 and M1.3 as the M1 can be found easily.