The Gecko Gauge SA903 gauges and supports fiber cement-board siding, including James Hardie's HZ5 series, for one-person installation with nearly no layout time. Working as a pair, the Gecko Gauge clamps to each siding course acting as a second set of hands to gauge and support the next course for nailing. Adjustable at 1/4 In. increments for 4 In. to 8 In. siding reveals. Will not scratch or mar pre-painted siding. Friction-cam mechanism supports full 12 Ft. fiber cement siding lengths. Set of 2 clamps.