The Gecko gauge SA903 gauges and supports cement-board siding for one-person installation with nearly no layout time. It is adjustable at 1/4 in increments for 4 to 8 in siding reveals. It won't scratch or mar pre-painted siding. The friction-cam mechanism supports full 12 ft cement-board siding lengths. It can be used with 5/16 in fiber-cement siding products, including James Hardie's updated HZ5 Series with new eased drip-edge profile.