The Acra Screed system is a revolutionary screed chair system that uses a reinforced concrete block as a base. Turning the block achieves four reinforcement cover heights. It offers a stable secure foundation for the screed rail without interference to the structural steel. Precision height adjustments can be made with a special drill tool that is accurate to 1/50 of an inch. Acra Screed Ltd. 44 1729 840000. .