Ford E-250 Floor Mystery

[wiggywam]

Has anybody seen anything like this before?
Its plywood subfloor, with these metal grills screwed into the van floor (last picture under the van).
Does anyone have any idea how I can get these out ? :a2:

 

[TheLetterJ]

That's E-track. Commonly used in cargo trailers. There's a million different fittings that click into there, pretty handy stuff.