Another nailing system is the soil nail and root technology (SNART). Here, steel nails are inserted very rapidly into a slope by percussion, vibration or screw methods. Grid spacing is typically 0.8 to 1.5 m, nails are 25 to 50 mm in diameter and may be as long as 20 m. Nails are installed perpendicular to and through the failure plane, and are designed to resist bending and shear (rather than tension) using geotechnical engineering principles. Potential failure surfaces less than 2 m deep normally require the nails to be wider near the top, which may be achieved with steel plates fastened at the nail heads. Plant roots often form an effective and aesthetic facing to prevent soil loss between the nails.