What are those little sheet-metal plug clamp thinggys called?

[CMars45000]

I was reading a write-up on sheetmetal replacement once and they were using these clamps that were these little round things...I dont know if the wend in a hole and clampped or if they went in the seam and clamped...The write up was on cab corners if I remember correctly...Any ideas?


Thanks,
Chris