A tube fitting (1A; 1B) that is capable of coupling a tube made from metal and provided with an annular portion (16; 26) upon an end portion thereof, to a mating member (MC1; MC2) by being installed upon an external periphery of the tube and by being fastened to the mating member (MC1; MC2) in a state of contacting the annular portion (16; 26), the annular portion (16; 26) projecting in a radially outward direction from the tube, the tube fitting (1A; 1B) comprising: a threaded portion (12; 22) upon which is formed an external thread (12a; 22a) that engages with an internal thread (12b; 22b) provided in the mating member (MC1; MC2); a contact portion (14; 24) that is provided at an end portion of the tube fitting in a direction of progression of the external thread (12a; 22a) when the tube fitting is being fastened, and that, when the tube fitting (1A; 1B) is fastened to the mating member (MC1; MC2), contacts the annular portion (16; 26) to press the annular portion (16; 26) against the mating member (MC1; MC2); and a resin coating layer (18; 28) provided over a coated region that includes surfaces (17; 27) of the threaded portion (12; 22) and the contact portion (14; 24); and wherein: a through hole (10; 20) extending in a direction parallel to the direction of progression is pierced through both the threaded portion (12; 22) and the contact portion (14; 24); wherein the tube fitting (1A; 1B) is characterized in that the external thread (12a; 22a) has an outer diameter of 9.53 to 14.0 mm, and the contact portion (14; 24) has an inner diameter of 4.98 to 8.44 mm; the resin coating layer (18; 28) includes a polyethylene based substance, a lubricant, and solid particles; and when mass per unit area w (g/m 2) is defined as being a value obtained by dividing a mass difference between a state with the resin coating layer (18, 28) and a state without the resin coating layer (18; 28) by a surface area of the coated region, the mass per unit area w satisfies a relation 0.79<w<10.07. a threaded portion (12; 22) upon which is formed an external thread (12a; 22a) that engages with an internal thread (12b; 22b) provided in the mating member (MC1; MC2); a contact portion (14; 24) that is provided at an end portion of the tube fitting in a direction of progression of the external thread (12a; 22a) when the tube fitting is being fastened, and that, when the tube fitting (1A; 1B) is fastened to the mating member (MC1; MC2), contacts the annular portion (16; 26) to press the annular portion (16; 26) against the mating member (MC1; MC2); and a resin coating layer (18; 28) provided over a coated region that includes surfaces (17; 27) of the threaded portion (12; 22) and the contact portion (14; 24); and wherein: a through hole (10; 20) extending in a direction parallel to the direction of progression is pierced through both the threaded portion (12; 22) and the contact portion (14; 24); wherein the tube fitting (1A; 1B) is characterized in that the external thread (12a; 22a) has an outer diameter of 9.53 to 14.0 mm, and the contact portion (14; 24) has an inner diameter of 4.98 to 8.44 mm; the resin coating layer (18; 28) includes a polyethylene based substance, a lubricant, and solid particles; and when mass per unit area w (g/m 2) is defined as being a value obtained by dividing a mass difference between a state with the resin coating layer (18, 28) and a state without the resin coating layer (18; 28) by a surface area of the coated region, the mass per unit area w satisfies a relation 0.79<w<10.07. a through hole (10; 20) extending in a direction parallel to the direction of progression is pierced through both the threaded portion (12; 22) and the contact portion (14; 24); wherein the tube fitting (1A; 1B) is characterized in that the external thread (12a; 22a) has an outer diameter of 9.53 to 14.0 mm, and the contact portion (14; 24) has an inner diameter of 4.98 to 8.44 mm; the resin coating layer (18; 28) includes a polyethylene based substance, a lubricant, and solid particles; and when mass per unit area w (g/m 2) is defined as being a value obtained by dividing a mass difference between a state with the resin coating layer (18, 28) and a state without the resin coating layer (18; 28) by a surface area of the coated region, the mass per unit area w satisfies a relation 0.79<w<10.07.