The invention concerns a threaded tubular component for drilling or working hydrocarbon wells, said tubular component having at one of its ends (1; 2) a threaded zone (3; 4) produced on its outer or inner peripheral surface depending on whether the threaded end is male or female in type, characterized in that at least a portion of the end (1; 2) is coated with a lubricating dry film (12) the matrix (13) of which comprises at least one migrating sliding agent (9) belonging to the oils or waxes family and principally distributed at the surface of the lubricating dry film (12) such that the coefficient of friction of the film (12) is less than 0.07 at loads of less than 40 N while the coefficient of friction of the film (12) is more than 0.1 at loads of more than 200 N.

The present invention relates to a viscosity index improver containing a copolymer (A) that contains, as essential constituent monomers, a fluorine atom-containing monomer (a) represented by the following formula (1) and a monomer (b) represented by the following formula (2), wherein the copolymer (A) has a solubility parameter of 8.1 to 10.0 (cal/cm.sup.3).sup.1/2, and a mass ratio (b/a) of the monomer (b) to the monomer (a) in the monomers constituting the copolymer (A) is 0.01 to 42: ##STR00001##
wherein R.sup.1 represents a hydrogen atom or a methyl group; R.sup.2 is a C2-C4 alkylene group; p is an integer of 0 or 1; q is an integer from 0 to 20, each R.sup.2 may be the same as or different from each other when q is 2 or greater; and Y is a monovalent group in which one or more or all of hydrogen atoms in a C1-C40 hydrocarbon group are replaced by fluorine atoms, and ##STR00002##
wherein R.sup.3 represents a hydrogen atom or a methyl group; X.sup.1 is a group represented by O or NH; R.sup.4 is a C2-C4 alkylene group; r is an integer of 0 or 1; s is an integer from 0 to 20, and each R.sup.4 may be the same as or different from each other when s is 2 or greater; and R.sup.5 is a C1-C40 hydrocarbon group.