The door of durin.

[Hot, crispy nice hobbit]

That ancient feud is actually never quite justified in the first place: Thingol had no claim of making Beren steal a Silmaril. He just wanted Beren to die trying, and got more than he bargained for. The Dwarves also had no claim over the Silmaril.

Nevertheless the friendship between Hollin and Khazad-dum is genuine, and not just for trade and craftmanship. When Sauron sacked Eregion for the Three Rings, and attacked Elrond's surviving forces, the Dwarves of Khazad-dum attacked Sauron's forces at the rear. (History of Galadriel and Celeborn, UT)

Still, it tickles to know that Celebrimbor poked fun at Narvi's expense...

Narvi: "My Lord Durin, the Western Gate is completed."
Durin: "Marvellous, what do these signs mean, though?"
Narvi: "Our friend Celebrimbor of Hollin drew them... they purportedly means 'Glorious halls'"
Durin: "Wonderful! Present him with that Mithril waistcoat our smiths prepared."