General description Royal Mail Large Letter PIP Cardboard Postal Boxes are high-quality, UK-manufactured corrugated boxes designed specifically for the Royal Mail 'large letter' postal system. These single wall die cut boxes are available in various sizes, including C4, C5, and C6, making them ideal for a range of mailing needs. Technical specifications Box style: Die cut Material: Corrugated cardboard Sizes: C6 Size - Internal: 160x110x20mm, External: 166x114x22mm C5 Size - Internal: 222x160x20mm, External: 228x164x22mm C4 Size - Internal: 332x245x22mm, External: 332x245x24mm Installation These boxes are easy to assemble with fold-over ends and "earlock" lids, allowing for quick and efficient packing.