PURPOSE: To provide a mail to fix a stretched thread for measuring the size by extending the thread, in a construction site and the like.

CONSTITUTION: A metal ring 3 in which a thread fixing tongue piece 2 opening at a small acute angle α in the direction of a nail head 1a is installed to the peripheral surface at the middle part of a nail 1 in the axial direction, so as to compose a thread fixing nail for extending a thread. Consequently, only by hanging a thread to the nail 1 without binding, the thread can be fixed securely by stretching strongly, and the thread can be removed from the nail 1 without cutting off.