Let's begin by their shape: well they look like big bolts, but pretty heavy bolts.
You know that you won't be able (unintentionally!) to damage them.
The goal is to remove the washer but the nut does not move, and here begins the puzzling part :-)
|Hard to distinguish which bolt it is...|
You can distinguish the Nipple bolt by the small ball at the bottom of the puzzle. Moreover, the Low number bolt has smaller protuberances on the nut.
These 2 puzzles have a different solution and they don't require external tools (however, for Low number bolt external tools help, but are not needed for solving the bolt!)
Both puzzles have a simple mechanism, but you know with Wil Strijbos, simple mechanism often means hard puzzles :)
For the price and the quality, I would advise you to buy them when Wil has some to offer.
You just need to wait for his new newsletter. By the way, it's been long time since we've not had any newsletter... :-) Big surprises may come sooner