They came with my Viper 301 and 300, so I know that they are HZ 1's,
Just suppose if you wanted to buy a set of them used, how would you be able to tell at a glance which ones they were without using a meter to see how hot they were? The HZ 1 and HZ 2 look identical on the website, as well as the HZ 3 and HZ 4. The only difference between them is the layout of the screws on the backside.
I suppose I should contact EMG and see what they say.