like following cleaning of fastener 10 a first metallic material 14 is applied to the cleaned portion in a first spraying operation the first metallic material 14 is preferably a metal or metal alloy similar to and which may have a modulus of elasticity substantially the same as that of the material of the threaded portion of the fastener satisfactory results have been obtained by applying a metallic material such as carbon steel on a carbon steel fastener a second metallic material 15 is thereafter applied to the first metallic material 14 in a second spraying operation to produce a composite metallic patch 13 the second metallic material that is illustrated is a metal or metal alloy having a modulus of elasticity lower than that of the first metallic material the resulting patch comprises an underlayer adjacent the fastener of the first metallic material e g steel and an overlayer of the second metallic material e g copper alloy satisfactory results have been attained by using materials such as copper alloys for the second metallic material in application where a complementary threaded steel element is contemplated it should be noted that the second material or first material if only a single material patch is to be utilized is chosen from a group of materials which are elastic materials and which will deform upon contact with the complementary threads it is preferred to have the patch deform rather than the complementary threads as illustrated in fig3 the spraying operation includes two flame spray guns 26 and 27 bolts 10 are successively moved past the guns 26 and 27 by a suitable conveyor facility not shown with their longitudinal axis disposed normal to the spray from the guns and the direction of movement of the bolts.