URGENT HELP PLEASE......pretensioners

[LOU'S CLIO]

i took the pretensioner off to fit to my new corbeau subframes,
i had to drill out a rivet to get this off the runner.

What does this bit do and where do i fit it to the new subframe?

any help would be great.

 

[JoedotwasT5phy]

is that not the seatbelt sensor, so it knows when you have it on?

 

[Riley!]

^+1