The figure shows a screw gauge (least count $0.01\ \text{mm}$) with its two faces touching. The datum line is at division $4$ of the circular scale, and the scale's zero is below the datum line. The same gauge then reads $2.86\ \text{mm}$ on a wire. What is the real diameter of the wire?

Fig. 1: A screw gauge with its two faces touching. Only the 0 mark of the sleeve shows. On the circular scale, the datum line is at division 4, four small marks above the scale's zero, so the zero lies below the datum line.