Whats Its

Found this thing today hunting an area that has produced IHP's, V and Buff nickels,seated dimes, mercs and Barber halves - So as you might imagine, when this dirt encrusted disc of metal came out of the ground today, I had quite a jolt of hope.
Experience has taught me to keep those hopes grounded, so it didn't last but a second, and as I rubbed the dirt off, it was apparent this is no coin.
Thought at first it was a big old button, but it is 'weigh' to heavy for that ... As you might be able to see from the pic, it has a "5" on it, so my guess is this was to an old weight set or something.
Still, a curious design for a weight piece, with the hollow crossed center.
Also found the remains of an old key, which fell apart even further as I tried to clean it off a bit.