Is this actually a necessary thing? And does anyone know the size of bolt that goes through it?

 

yes you have to have it. the bolt size? any bolt that will fit threw with a nut on the other side.

 

That clamp holds the tierod tight around the tierod end. Without it the threads within will loosen and you could have an unsafe situation on your hands.

Look at the tierod.. it's not solid all the way around it's diameter.

 

I believe its a 5/16th bolt with a 1/2" head