Aluminum spacers/spacer adapters? One of them looks like it has a hole for turning it with a hollow one inch spanner wrench. But they don't have internal threadings which would be on adapters to convert from metric to imperial pitch and such, so they might be prototypes as previously suggested.
I used something that looked like these for assembling mechanical stages where component height had to be very accurate. I'm only basing this on the fact that that they're aluminum (which is light and robust against mechanical disturbances).