It’s one thing to make the Gleipnir, but it’s another to get it on Fenrir. The wolf is not dumb. The previous chains looked weak enough for him to break, and his strength had grown, but he’s suspicious of how thin Gleipnir is, and is wary of some hidden art that makes the ribbon stronger than it appears. However, in steps Tyr, who still has both hands at this point. Tyr offers to place his hand in Fenrir’s mouth as promise that they will remove Gleipnir. If they don’t, Fenrir gets a free hand.
Okay, time out.
So at first glance, this myth might run contrary to what I said about keeping oaths, earlier. The gods are clearly betraying their word, right? It’s all a lie, a sham, in order to trick Fenrir into doing what they want. Clearly, this would be stepping into Loki’s domain, and it should be impossible for the gods to pull this off. After all, it said that Frigga was incapable of lying, so how can it be that the gods are able to do this to Fenrir?
Is Tyr somehow exempt from this idea? This doesn’t stand to reason as Tyr is the most honorable warrior among the gods. His word is the standard by which oathkeeping should aspire to, so it doesn’t make sense that Tyr is exempt. And he’s not. In fact, no deception took place.
What was established with Fenrir was not a lie, but a bargain, a contract. The terms were straightforward, we put the chain on you, and you hold Tyr’s hand for ransom. We take the chain off, you don’t chomp down on his hand. We leave the chain on, you chomp down on the hand. It’s not the fault of the gods that Fenrir didn’t understand the legal loophole he had stepped in. For Tyr’s part, he fully understood what was asked of him, and willingly sacrificed his hand in order to keep Fenrir captured. This was a sacrificial bargain similar to Odin giving up his eye to Mimir.
While Gleipnir is impossibly strong, Fenrir’s strength is constantly growing. Also, time is not on Gleipnir’s side. Anything made will weaken over time. Gleipnir will hold until Ragnarok, when all things are destroyed, but that is the limit to even dwarven craftsmanship.
Bonus! J.R.R. Tolkien paid homage to Tyr’s sacrifice with the story of Beren and Luthien in The Silmarillion. In order to win fair Luthien, Beren had to retrieve one of the famed silmarils, which he did. Unfortunately, on the way out, he brandished it at the wolf Carcharoth in order to scare it off, but instead it decided to chomp on it. Beren gets the last laugh as he goes to the king, claiming that the Silmaril rests in his hand. It’s still inside the wolf, but he still kept his word. (Seriously, everyone should go read the Silmarillion. I might even spend some time doing stories from it since it’s such a wonderful book).