【what is the function of slots provided in the castle nut?】

what is the function of slots provided in the castle nut?https://pnimg.net/w/articles/4/685/29e41f0c58.jpg|https://s.pnimg.net/bFThoCoAdM86swKvC38yCG8BcsR3MmZgZukb_lpDQ6A/pr:article-body/aHR0cHM6Ly9wbmlt/Zy5uZXQvdy9hcnRp/Y2xlcy1hdHRhY2ht/ZW50cy8wLzY4NS8y/OWY1MTI2NWFhLmpw/Zw.webp|https://s.pnimg.net/apH8pmoJDeuxF3KFjkuFInF55-9GEnvqY8Zpl269Kbk/pr:article-body/aHR0cHM6Ly9wbmlt/Zy5uZXQvdy9hcnRp/Y2xlcy1hdHRhY2ht/ZW50cy8wLzY4NS8y/OWZhNDk2MjZhLmpw/Zw.webp|https://s.pnimg.net/6vHdAGKNOHW1BqZiJ5sYPahoNAutMCKWYpaZcUyFM5s/pr:article-body/aHR0cHM6Ly9wbmlt/Zy5uZXQvdy9hcnRp/Y2xlcy1hdHRhY2ht/ZW50cy8wLzY4NS8y/OWZjYmNlNGEzLmpw/Zw.webp