Concessional excise duty rate for specified gun carriage tyres and tubes capped at a lower ad valorem rate. Under powers under section 5A, the Government exempts gun carriage tyres (sizes 8.25-19 LR 5-9PR and 8.25-19 LR 5-10PR) under sub heading 4011.70, and their tubes under sub heading 4013.70, from so much of the excise duty leviable under the Tariff as is in excess of the duty calculated at the rate of 20% ad valorem.