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 resilient compression elements extending from the spacer block. The one or more resilient compression elements can be a joist leg configured to engage a joist, or it can be vertically compressible toward a first plane that is transverse to a vertical axis of the spacer block so that portions of it can compress from an open mode to a compressed mode and fit within, then forcibly expand within the groove, thereby securing the spacer block in a position adjacent the groove to establish a gap between the board and another board. A related method of use also is provided.