Gregory, I'm guessing you mean type f and type g. There is no type j that I'm aware of. The only difference is type f the safety functions as both a safety and decocker. The type g the lever is just a decocker. Other than that they're identical. Hope this helps and you're very welcome

Gregory, on type F, the safety also functions as a decocker, type G is a decocker only model. They are exactly the same other than that. Have a great day!

Gregory, Type F safety functions as both a safety & decocker model and the Type G is a decocker only model. The firearms between Type F and Type G are otherwise identical. Cheers and stay safe!