Classification of cotton fabrics ordered reclassified under tariff heading to ensure uniform assessment and administrative consistency, not retrospective. The Central Board, invoking Section 37B, directs that grey cotton canvas, cotton ducks, cotton tyre cord fabrics and cotton belting fabrics shall henceforth be classified under Heading No. 52.05 of the Central Excise Tariff to ensure uniformity; the order does not alter past closed assessments and Collectors must issue trade notices and inform officers to effect consistent assessment practice.