The Thule culture developed 900 –1000 BP on the coast of Canada and most northerly Greenland. These people specialized in hunting seals and walrus on sea ice using harpoons, as well as building igloos. First they settled exclusively on the West Coast of Greenland. They utilized boats, developed the kayak in order to pursue their prey onto water. They also hunted with bow and arrow.

Graphik from „Eskimos“, People in the land of long days by from Wally Herbert, Österreichischer Bundesverlag Wien, 1976

The harpoon blades used during the Thule Culture where already the blades or harpoon heads used for hunting from the kayak. They correspond to the "loose on the shaft" principle. After been hitten the animal tries to loosen itself from the harpoon. In doing this it shakes itself, the head of the harpoon stays in the animal whilst the shaf loosens itself out of the hole drilled into the shaft. Size of the harpoon head (Nr.6) ca. 70mm.

Copy from the book:
DEN GRØNLANDSKE KAJAK OG DENS REDSKABER
Nyt Nordisk Forlag Arnold Busk 1975