A stepped tapper hole is inspected with a probe using a coordinate measuring machine as shown in the figure. The probe diameter is 1.5 mm. At height y = 40 mm from the bottom, the diameter of the circle is obtained as 50 mm, at height y = 60 mm from the bottom, the diameter of the circle is obtained as 60 mm and at height, y = 0 mm, the diameter of the circle is obtained as 20 mm. The diameter of the hole at y = 5 mm from the bottom will be ___ mm. (The probe size while measuring the tapper diameter is not compensated)