What’s missing here?

[CG]

I was looking for something to dump in my electrolysis bucket and remembered I had this extra set of bucket seat sliders. After looking at them I decided these are very nice and have no need to be electrified (ha). I did decide to see how they worked. They slide fine but the release arm was sticky, PB Blaster fixed that. Looking at the passenger side though I seem to be missing the track locking pieces. Can someone tell me what I should have in there? I feel like I saw that someone was selling these but maybe only drivers side? Any help is appreciated.