A spanner comprises a box end that has an inner periphery consisting of a number of wall faces to define a first polygonal receiving space. The proposed logic units, as separate units or cluster of units, which are mainly comprised of look-up tables, multiplexers, and a latch, implement functions such as addition, subtraction, multiplication, and can perform as shift registers, finite state machines, multiplexers, accumulators, counters, multi-level random logic, and look-up tables, among other functions. are further added, at not higher than the Ac3 transformation point, and applying reducing at an average rolling temperature of m and a total reduction ratio Tred within s temperature range of from 400 to Ac3 transformation point, with di, m and Tred being in a relation satisfying a prescribed equation.