Sounds like what you got is a Seymour Duncan JB Trembucker. The tb4 has the same characteristics of the JB pickup but with slightly wider pole spacing to accomodate Floyd Rose and other types of locking tremolo systems. That could be good or bad depending on the type of guitar you're installing it into, and more specifically what type of bridge setup your guitar has.
I installed it on my schecter. And the pole pieces fits right below the strings. I love how it sounds. The previous pickup was sh6 which i liked too, but I think this jb tone is what i've been looking for.
So, it means that my jb is genuine right? Thanks God