A converting module for converting a first analog voltage into a digital output value includes a comparator for comparing the first analog voltage with a threshold voltage and generating a comparison result, the threshold voltage corresponding to a first group of digits containing at least one digit. , and soaking aluminum or an aluminum alloy in the treating solution; a piston having a surface coated with a film consisting of a mixture of NH4MgAlF6 and MgAlF51. A deficiency registering circuit registers the determined address information in the position memory circuit. Apparatus is included for facilitating lifting the sample from the slab, after curing. The severing means includes a spindle member and a loop shaped member axially movable relative to one another in response to actuation of said operating mechanism so as to clamp an end portion of said thread insert between an end portion of said spindle member and said loop shaped member.