My camera won't fit into my tripod?

i have a canon eos 550d, and i found my dads old tripod but the screw on the head won't fit into the camera's hole it seems to be too big. also i removed the head part because someone else said on theirs underneath the head was a smaller screw that would fit the camera, but their was nothing their. if it helps on the bolt it says D G 8.8 im not sure what that means though also its made by Manfrotto. thanks in advance for any answers!