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: C4 Internal dimensions: 332 x 245 x 22 mm External dimensions: 332 x 245 x 24 mm Other sizes available: C6 (Internal: 160 x 110 x 20 mm, External: 166 x 114 x 22 mm), C5 (Internal: 222 x 160 x 20 mm, External: 228 x 164 x 22 mm) Installation These boxes are easy to assemble with fold-over ends and "earlock" lids, allowing for quick and efficient packing.