Threaded joint

A threaded joint comprising:

• a pin having an externally threaded part comprising a first externally threaded section and a second externally threaded section across a step on an outer periphery on a distal-end side of a first steel pipe or tube;
• and
• a box having an internally threaded part comprising a first internally threaded section and a second internally threaded section across the step on an inner periphery on a distal-end side of a second steel pipe or tube,
• the externally threaded part being screwed to the internally threaded part to join the pin and the box, wherein
• the first externally threaded section is provided on the distal-end side of the first steel pipe or tube with respect to the second externally threaded section,
• the first internally threaded section is provided on the distal-end side of the second steel pipe or tube with respect to the second internally threaded section, and
• assuming:
• a region in which the first externally threaded section is screwed to the second internally threaded section is defined as a first thread sequence, and a region in which the second externally threaded section is screwed to the first internally threaded section is defined as a second thread sequence;
• a length of the first thread sequence in the axial direction of the steel pipe or tube is defined as L1, and a length of the second thread sequence in the axial direction of the steel pipe or tube is defined as L2;
• in the pin, a cross-sectional area in the radial direction at an end position on the opposite side to a distal end of the pin in the first thread sequence is defined as P1, and a cross-sectional area in the radial direction at an end position on the opposite side to a distal end of the pin in the second thread sequence is defined as P2;
• and
• in the box, a cross-sectional area in the radial direction at an end position on the opposite side to a distal end of the box in the second thread sequence is defined as B1, and a cross-sectional area in the radial direction at an end position on the opposite side to a distal end of the box in the first thread sequence is defined as B2,
• then L1, L2, P1, P2, B1, and B2 satisfy the following Formula (1) and Formula (2):
• (P2, B2)min≤P1/{L1/(L1+L2)} (1)
• (P2, B2)min≤B1/{L2/(L1+L2)} (2)
• where (P2, B2)min represents P2 or B2, whichever is smaller.