Abstract: A spacer or gauge is provided for maintaining accurate spacing between adjacent wooden boards of a deck, patio, walkway or the like incident to the performance of a nailing operation. The spacer is formed from two members, namely, an elongated leg welded in transverse relationship to a support member. A lower flat surface of the support member rests upon and spans adjacent deck boards while a lower leg portion of the elongated leg has opposite substantially parallel space defining surfaces which are spaced a predetermined distance from each other. The space defining surfaces are contacted by opposite edges of the deck boards, and the support member has a pair of apertures which allows a person to view the deck board edges and ascertain that the same are in contact with the space defining surfaces.