To strength the connection by folding and caulking the tip of a long nut inserted in a hole provided on a plate to caulk to the peripheral part of the hole and also weld it to the plate, and providing a partial clearance between the hole and the long nut.

A hole for inserting the tip of a long nut 3 is formed in the center of a rectangular plate 2, and four clearances 5 consisting of cutout parts are arranged on the peripheral part of the hole, and ribs 6 are formed in the long axial direction on both side edges of the plate 2. The tip of the long nut 3 is inserted to the hole of the plate 2 and caulked so as to curve outward in skirt form to form a skirt-like ring 9 consisting of the tip of the long nut 3 on the peripheral part of the hole of the plate 2. This fitting 1 is dipped in a preservative solution to perform a rust preventing treatment. Since the inner part of the skirt-like ring 9 communicates with the clearances 5 of the plate 2, the preservative solution flowing into the skirt-like ring 9 flows out through the clearances 5. Accordingly, the preservative solution can be prevented from being left to rust the fitting.