Arris Rail 2.4m 8ft 75mm x 75mm 2ex Natural / Green Arris Rail suitable when using brackets to fit to posts. Pressure Treated Brown. We do not recommend you install a fence panel longer that 8ft You, Will Need Galvanised Arris Rail Brackets To fix to Wooden Posts. TANALITH Extra is an effective water repellent additive that can be used with TANALITH wood preservative within the treatment process. It gives an added built-in weathering protection to the treated timbers. TANALITH Extra treated timbers have all the same preservative protection properties as TANALITH treated timber. The water repellent also helps maintain the dimensional stability of the treated timbers.