Something tells me that if we are all having trouble describing it, finding pictures of it, or attributing a name to it (though, now I guess we might be able to call it a "J hook" Mason), then it's gotta be a more uncommon machine-made jar. I've only seen one or two pictures/listings of this jar. But yeah, it's definitely machine-made, 1910-1920 give or take. Even if only for a short time, it still would have been made in mass, so there are more out there for sure. It's a pretty jar though, I really like the diagonal orientation and the J hook.