In regions that use the US Letter paper format (); United States, Canada, and in part Mexico and the Philippines), a three-hole standard is widely used. The holes are positioned symmetrically, with the centers apart. The diameter of the holes varies between manufacturers, with typical values being . The value is most commonly used, as it allows for looser tolerances in both ring binder and paper punching. The distance of the hole center to the paper edge also varies, with being a typical value. Unlike ISO 838, this 3-hole system appears to have no well-established official specification, and is a de facto standard established by custom and tradition. It can only be applied to paper formats that are at least high.