Normal machinery variances in the envelope manufacturing industry are +/- 2mm. This occurs because as machinery runs, it heats up, and metal expands. In addition, normal wear in cylinders and bearings can cause subtle variations in cutting location and folding scores. As a result, your envelope may be slightly larger or slightly smaller than you ordered. The window position if applicable may be slightly off. The key word here is “slightly” because 2mm” is very small. We will along with our envelope manufacturer make every attempt to hold tolerance, but if your application requires an exact measurement, it’s best to contact us prior to placing orders in order to check that the product will satisfy your requirements.