Here's how it works. Someone will start a thread saying something like this:

Check out my new fingerbox I custom-made for recreational use. I think it turned out pretty well.

or:

Does anyone know of a website where I can order a fingerbox lid replacement? Mine broke and I don't think I can last much longer without daily use. I'm really jonesing for the old fingerbox. I'm thinking about going for one of the newer german models. Anyone have any experience with them?

Some of the posts are super elaborate, like:

This is a cast-iron fingerbox my WWII veteran grandpa gave me when I was a kid. I've used it every day since. Note the gold guilt and inlay. They just don't make 'em like they used to, right guys?

To which someone will inevitably reply:

WTF is a fingerbox?

The fingerbox is just a troll. They don't exist... or do they?

I did a bit of googling and found that there is a Japanese artist identified with fluxus (an avant-garde artistic movement started in the 60s) named Ay-O, who actually created a series of "Fingerboxes."

Ay-O would build a box with a finger-hole and put something inside, like feathers, thumbtacks or ball bearings. Gallery attendees were intended to stick in their fingers and I guess try to figure out what was inside. Art!

I found a blog post about fluxus that describes the fingerboxes:

Playing upon the subject's irresistible desire to "touch," Ay-O's box features a finger-sized hole with various hidden materials placed inside (different in each, like nylon stocking, rubber or nails) to challenge tactile perception. In its raw state, Ay-O's Finger Box might ultimately have been dismissed as an eccentric and largely illegible item of Fluxus pranksterism; its unassuming form, proposing an action that seems like a futile one-liner.

So the original art seemed like a prank itself. Maybe this was the inspiration for the first anonymous person who claimed they used a fingerbox growing up.

But the prank has evolved beyond Ay-O's art. This photo from a fingerbox thread appears to be something from Home Depot. It seems like people are just searching for images of boxes with holes in them to use in the trolling threads.

This actual Ay-O fingerbox is selling for £1,450.00, probably a touch too high for any 4channer to buy it just to advance the meme. But with this price and description, maybe they think this box actually does something too:

7.5 x 7.5 x 7.5cm (approx.) cardboard box with gummed on black and orange printed paper labels designed by Maciunas: Items to be inserted in Ay-o boxes ranged from nylon stockings, feathers or even thumb tacks - are you willing to take the risk?

This box was issued in a small edition size as an announcement object for Ay-o's 6 foot cube tactile box that was shown at the gallery (and also promoted the deluxe variants that were for sale).

The fact that this announcement box was such a nice object within itself and very similar to the deluxe edition meant that the sales of the latter items suffered. Slight wear and tear at edges but otherwise very good. Rare.

Here's my hypothesis: Someone found a picture of a box with finger-sized holes in it during a random Google Image Search. The person thought it might be funny to troll 4chan with it, so he posted the image along with a caption like, "Check out my fingerbox. Jealous?" Then dozens of people saw the thread and tried to figure out what it was all about, then they found all of Ay-O's fingerboxes, so they integrated those into the mythology of this troll.

The fingerbox is a growing meme. The trick is to offer elaborate descriptions of the fingerbox, while remaining vague about its intended use. Some trolls imply that they use the fingerbox for sexual purposes. Others have hinted that it's meant for relaxation or play.

The more detailed the description, the stronger the troll. Before long, other posters will be saying things like:

THIS SOUNDS SO STUPID. SOMEBODY BETTER EXPLAIN. SERIOUSLY WTF...

Why do people do this? The same reason people get satisfaction from any kind of prank or troll. There's a weird satisfaction that goes along with convincing someone that they're missing out on something important, especially when that thing is totally made up.

A few have gone so far as to craft their own fingerboxes just to take the troll to the next level. Scope out this primitive model.