Technical 55-56 Olds seat question

I got a seat from a donor car and had them redone. I can’t figure out how the driver side back connects. The p***enger side has a round peg sticking out and the backrest clearly slides on it. The driver side does not. Can any one help? A picture would help a lot.

 

Did you pull off the covering, and look to see if there is the remains of where a stud used to be?

 

thank you! I pulled the hog rings off and it was there. The upholstery guy covered them. Weird because he pointed out the stud missing.

 

upholstery guys live in a non-mechanical world...gotta watch out for them!