i would like to put a JB Jr in the middle of my Ibanez rg 1570 but the shape of the hole is different.it is like the Hot rails.Does it really matter? or will i just have a "smal gap" in my guitar? :question:
That "small gap" is absolutely normal and won´t cause any problems.
Most single coil routs follow the "vintage design" of classic single coils (with the "ear" on the bridge side), the JBJr and some others just don´t need the ear and therefore don´t have one