... a helm of Húrin once hewn in wars
when he battled with Beren as brother and comrade
against ogres and Orcs and evil foes.
Grey-gleaming steel, with gold adorned
wrights had wrought it, with runes graven
of might and victory, that a magic sat there
and its wearer warded from wound or death,
whoso bore to battle brightly shining
dire dragon-headed its dreadful crest.

...
Then a thought was thrust into Thingol's heart,
and Túrin was called and told kindly
that his mother Morwen a mighty thing
had sent to her son, his sire's heirloom,
o'er-written with runes by wrights of yore
in dark dwarfland in the deeps of time,
ere Men to Mithrim and misty Hithlum
o'er the world wandered; it was worn aforetime
by the father of the fathers of the folk of Húrin
whose sire Gumlin to his son gave it
ere his soul severed from his sundered heart -
"'Tis Telchar work of worth untold,
its wearer warded from wound or magic,
from glaive guarded or gleaming axe.

(HoME III, The Lays of Beleriand, The Children of Húrin, 637-645, 667-680)

Then Thingol received Túrin, and took him even to his own fostering, in honour of Húrin the Steadfast; for Thingol's mood was changed towards the houses of the Elf-friends. Thereafter messengers went north to Hithlum, bidding Morwen leave Dor-lómin and return with them to Doriath; but still she would not leave the house in which she had dwelt with Húrin. And when the Elves departed she sent with them the Dragon-helm of Dor-lómin, greatest of the heirlooms of the house of Hador.

(Silm, Chapter 21, Of Túrin Turambar)

Dragon-helm of Dor-lómin - Heirloom of the House of Hador, worn by Túrin; also called the Helm of Hador. 114, 251, 260, 284

(Silm. Appendix)

The Helm of Hador was given into Thingol's hands. That helm was made of grey steel adorned with gold, and on it were graven runes of victory. A power was in it that guarded any who wore it from wound or death, for the sword that hewed it was broken, and the dart that smote it sprang aside. It was wrought by Telchar, the smith of Nogrod, whose works were renowned. It had a visor (after the manner of those that the Dwarves used in their forges for the shielding of their eyes), and the face of one that wore it struck fear into the hearts of all beholders, but was itself guarded from dart and fire. Upon its crest was set in defiance a gilded image of the head of Glaurung the dragon; for it had been made soon after he first issued from the gates Morgoth. Often Hador, and Galdor after him, had borne it in war; and the hearts of the host of Hithlum were uplifted when they saw it towering high amid the battle, and they cried: "Of more worth is the Dragon of Dor-lómin than the gold-worm of Angband!"
But in truth this helm had not been made for Men, but for Azaghâl Lord of Belegost, he who was slain by Glaurung in the Year of Lamentation. [4] It was given by Azaghâl to Maedhros, as guerdon for the saving of his life and treasure, when Azaghâl was waylaid by Orcs upon the Dwarf-road in East Beleriand. Maedhros afterwards sent it as a gift to Fingon, with whom he often exchanged tokens of friendship, remembering how Fingon had driven Glaurung back to Angband. But in all Hithlum no head and shoulders were found stout enough to bear the dwarf-helm with ease, save those of Hador and his son Galdor. Fingon therefore gave it to Hador, when he received the lordship of Dor-lómin. By ill-fortune Galdor did not wear it when he defended Eithel Sirion, for the assault was sudden, and he ran barehead to the walls, and an orc-arrow pierced his eye.
But Húrin did not wear the Dragon-helm with ease, and in any case he would not use it, for he said: "I would rather look on my foes with my true face." Nonetheless he accounted the helm among the greatest heirlooms of his house.
Now Thingol had in Menegroth deep armouries filled with great wealth of weapons: metal wrought like fishes' mail an shining like water in the moon; swords and axes, shields an helms, wrought by Telchar himself or by his master Gamil Zirak the old, or by elven-wrights more skilful still. For some things he had received in gift that came out of Valinor and were wrought by Fळanor in his mastery, than whom no craftsman was greater in all the days of the world. Yet Thingol handled the Helm of Hador as though his hoard were scanty, and he spoke courteous words, saying: "Proud were the head that bore this helm, which the sires of Húrin bore."
Then a thought came to him, and he summoned Túrin, an told him that Morwen had sent to her son a mighty thing, the heirloom of his fathers. "Take now the Dragonhead of the North," he said, "and when the time comes wear it well." But Túrin was yet too young to lift the helm,..

[4] With this description of the Helm of Hador compare the "great masks hide ous to look upon" worn by the Dwarves of Belegost in the Nirnaeth Arnoediad, which "stood them in good stead a gainst the dragons" (The Silmarillion p.193). Túrin afterwards wore a dwarf-mask when he went into battle out of Nargothrond, "and his enemies fled before his face" (ibid. p. 210). See further the Appendix to the Narn, pp. 162-3 below.

(UT, Narn i Hín Húrin)

It may be noted here that it was my father's intention to extend the history of the Dragon-helm of Dor-lómin into the period of Túrin's sojourn in Nargothrond and even beyond; but this was never incorporated into the narratives. In the existing versions the Helm disappears with the end of Dor-Cúarthol, in the destruction of the outlaws' stronghold on Amon Rûdh; but in some way it was to reappear in Túrin's possession at Nargothrond. It could only have come there if it had been taken by the Orcs that carried Túrin off to Angband; but its recovery from them at the time of Túrin's rescue by Beleg and Gwindor would have required some development of the narrative at that point.
An isolated scrap of writing tells that in Nargothrond Túrin would not wear the Helm again "lest it reveal him", but that he wore it when he went to the Battle of Tumhalad (The Silmarillion p.212, where he is said to have worn the Dwarf-mask that he found in the armouries of Nargothrond). This note continues: For fear of that helm all foes avoided him, and thus it was that he came off unhurt from that deadly field.
It was thus that he came back to Nargothrond wearing the Dragon-helm, and Glaurung, desiring to rid Túrin of its aid and protection (since he himself feared it), taunted him, saying that surely Túrin claimed to be his vassal and retainer, since he bore his master's likeness on the crest of his helm.
But Túrin answered: "Thou liest, and knowest it. For this image was made in scorn of thee; and while there one to bear it doubt shall ever assail thee, lest the bearer deal thee thy doom."
"Then it must await a master of another name," said Glaurung; "for Túrin son of Húrin I do not fear. Otherwise is it. For he has not the hardihood to look me in the face, openly."
And indeed so great was the terror of the Dragon that Túrin dared not look straight upon his eye, but had kept the visor of his helmet down, shielding his face, and in his parley had looked no higher than Glaurung's feet. But being thus taunted, in pride and rashness he thrust up the visor and looked Glaurung in the eye.

(UT, Narn i Hín Húrin, Appendix)