A fastener unit and related method for securing a board to a support is provided. The fastener unit includes a spacer block, a grip element extending from the spacer block and configured to fit in and engage a groove of the board, and one or more board engagement elements extending from a portion of the spacer block. The board engagement elements can clamp the board, between an upper and/or lower surface of the board and a groove of the board, thereby securing the spacer block in a position adjacent the groove to establish a gap between the board and another board. Related methods of use also are provided.