ok i have gotten a new steering wheel for my boat but i am having problems. I have a 89 bass chapion and i cant get the old steering wheel off

I took the actual steering wheel off by taking off the 6 screws but i cant get the back thing off. I took the middle made nut off and it doesnt just slide off. I dont know if theres a pin hidding somewhere or another bolt of nut somewere. anyone know what i might do. thanks matty