Abstract: An article of sandal includes a sole structure and a strap secured on the sole structure. The sole structure has an upper surface and a lower surface and an aperture penetrating through the sole structure and exposing an engaging surface between the upper surface and the lower surface of the sole structure. The strap is secured on the upper surface of the sole structure by having a joining plug assembled in the aperture. The joining plug has a blocking portion and a pillar portion connected to a top surface of the blocking portion. The top surface of the blocking portion has a plurality of protrusions that are in direct contact with the engaging surface of the sole structure.