The mouth of the plane is milled with a slot cutter in two stages. One cutter first makes an initial cut across the sole at the exact center of the planes mouth . All the additional components —the "Y"- yoke lever, adjustment knob, stainless steel lateral adjustment lever, and so on —are likewise produced in preparation for final assembly. One person assembles the various planes in a small assembly room. This person takes each of the components and checks for any surface defects in any of the parts. Then, before installing the cutting iron assembly, each iron is tested for hardness using a Rockwell scale. A testing block is used to first set the machine calibration to ensure each of the irons tests out between Rc60 - 62. The carefully expedited production methods used to produce the Clifton planes ensures that rejections are kept to a minimum. Even those planes that are rejected are vastly superior to any ever produced by the old producing companies such as Stanley or Record. With quality checked and the plane assembly completed, only two tests remain.