Shear key structure

Disclosed is a shear key structure which, when connecting a plurality of steel pipes longitudinally, prevents these steel pipes from turning relative to one another about the axes thereof. This shear key structure is provided with a screw fixed to a joint member which establishes a connection between the aforementioned plurality of steel pipes; a key body wherein there is formed, in the bottom section, a recess provided with a through hole for inserting the aforementioned screw; a nut which is threaded onto the aforementioned screw and is disposed in the aforementioned recess; and an elastic piece provided to the gap between the outer periphery of the aforementioned nut and the sidewall of the aforementioned recess.