My doorcard screw heads are smaller than the ones pictured. I want to say the doorcard screws are more similar to the ones that hold the front access panels. Yea, I haven't seen that type of screw in my 05 Elise. I would check the doorcard screws, seat bolts(doubtful as that seems too small for it), or the floor mat screw. It's possible they replaced one of the OEM screws they had with that one so hard to say. Good luck.
Wow. Thanks for the comments. I’ve been away from my computer for a week or two. Yep. It’s aluminum and has a really large Allen recess. Way larger than the door card screws. I’ll check the roof cable, but I’m guessing that’s not aluminum. It turned up on the passenger seat when a guy was getting it at the track for a ride-along. Now I’m starting to think it fell out of his helmet.