A device for affixing a decking member to a joist includes a jig body positionable atop a pair of spaced-apart decking members positioned atop a joist. The jig body has an angled bore having a bottom end extending through a bottom face of the jig body, the bottom end of the angled bore in communication with the space between the decking members. The angled bore defines a centerline extending through the space to a position on the side of the first structural member. The angled bore is for receiving a fastener drivable therethrough into the first structural member's side face, through the first structural member's bottom face, and into the second structural member's top face.