A method of fastening a lower end portion of a siding board in installing vertical board siding by using posts located adjacent to each other, said method comprising the steps of:
- attaching a main metal fitting having a flat substrate to a portion of one of the posts where the lower end portion of the siding board is to be fastened;
- mounting an auxiliary metal fitting to said main metal fitting so that a first horizontal portion of said auxiliary metal fitting rests on an upright portion formed at a lower end portion of said flat substrate and extending in a lateral direction of said flat substrate;
- and
- griping a side edge of the siding board with an engaging portion located at a distal end of another upright portion formed along a longitudinal direction of said flat substrate, to thereby fasten the siding board to said main metal fitting while rendering the lower end portion of the siding board to be received by a second horizontal portion of said auxiliary metal fitting.