Morticed Arris Rail 2.4m 8ft 75mm x 75mm 2ex Arris Rail suitable when Morticed fence posts. We do not recommend you install a fence panel longer that 8ft. 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.