I know nothing about what aircraft flew from that field at any given time, but if it is from a jeep, I'd batch it from 1941 or so through the early 60's.
However - I just thought of a loooooong shot - but since I have no basis for making this guess other than 'inspired guess', I'd follow it up with research. But since from your first post it sounds like a training field, I tried to think of what use it could be on an aircraft. It might have been used to secure the canvas hood over the cockpit of an Army (since it's dark green) biplane for instrument-only training flights.
While the biplane cockpit guess is more of a wish than a guess - and it's more likely that it comes from a much more mundane origin - I wouldn't jump to conclusions. I just wanted to throw it out there as a possibility. I don't even know how they secured those canvas hoods down, but I believe Army planes in the 20's and 30's were a shade of dark green. Who knows? Keep us posted on what else you might find out!
How did you come across it? Was it close to a building: Out in the middle of nowhere? On the field or near it? Was it on the surface or under dirt? If under dirt, how deep? Try to find out how the field's configuration evolved over the years - was the spot where you found it at one time occupied by hangars, or a runway, or empty land? How complete are field records? Could there have been a crash whereby this bit was ejected and lost? Granted, it looks like a jeep part too, but you never know. Is there a museum around where you could compare it to a jeep from the 40's to see if it matches up with those parts? Get going, Sherlock Holmes! This could be fun!
One thing's for sure, though - it isn't from any uniform or web gear I've ever seen. Without a top-down view it's hard to say, but it looks like a screwhole on either side to bolt it down to some kind of larger object - presumably vehicle (or aircraft).