What did the clothespin symbolize to Clay in Bridge of Clay?

Bridge of Clay is a 2018 novel written by Markus Zusak. It tells the story of five brothers, Clay, Matthew, Rory, Henry, and Tommy Dunbar, who must come to terms with the death of their mother and the subsequent disappearance of their father.
The clothespin is a recurring symbol throughout the novel. Clay’s mother is found lying in the garden with her eyes closed. Clay realizes that the clothespins on the washing line are the last things she will have seen. He takes one of these pins and puts it in his pocket. He then holds it in his hand as she is dying. Clay carries this pin with him at all times. It serves not only as a reminder of his mother but also of the guilt that he feels about her death.