When Loki had Sif's hair, Freyr's ship Skidbladnir and Odin's spear Gungni done by the sons of Ivaldi, he bet his own head with Brokk that his brother Eitri wouldn't have been able to make items worth as much as the ones above.
Eitri succeeded in making the golden ring Draupnir, Gullinbursti and the hammer Mjollnir and Brokk won the bet, but Loki didn't allow him to take his head because he would have hurt his neck, not included in the bet.