A water-soluble lubricant including a cyclic compound (A) having a ring structure (a) including at least one substructure represented by the following formula (i) or (ii):

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in the above formula, * represents a binding site. The water-soluble lubricant is used in an aqueous metalworking fluid and in a method of metalworking.

An agent for forming a solid lubricating coating film on a tightening surface of a thread portion, in which a solid lubricant is dispersed in a binder resin as a matrix component, a main component of the solid lubricant is melamine cyanurate, and an average particle diameter of the melamine cyanurate is 0.1 m or more and 10.0 m or less, the binder resin contains an alkyd resin and nitrocellulose, and the alkyd resin and nitrocellulose are contained in an amount of 85 wt % or more of the total binder resin component weight, and a total weight of the solid lubricant is 10 parts by weight or more and 100 parts by weight or less based on 100 parts by weight of a total weight of the binder resin.