Second Class mail aims to deliver your letter or packet by the third working day after posting including Saturday. Large Letter mail is defined as mail which is between C5 (229mm x 162mm) & B4 (353mm x 250mm) in size which is more than 5mm but less than 15mm thick. Weight should not exceed 1.4kg. Millions of people use Second Class mail every day to send Letters Packets & other small items. You will receive 8 packs of 4 second class large letter stamps totalling 32 stamps.