Rail Forend

i bought a hogue rubber forend for my mossberg 500 and the rail thing is not workin right?
all i know is that its rubber and the pieces that u unscrew and take off to slide into the new forend doesnt come out far enough to screw it back on, its a knoxx
Take it to a gunsmith and see if you’re not doing something right. He shouldn’t charge more than 15-20 dollars to install it….if he can.
I remember reading that there are a couple of specific m500-m590-maverick models that Knoxx copstock ascessories don’t work with!