Abstract: When forming a dowel section by performing press working on each of portions constituting side walls of a buckle base member, a die having a negative clearance with a punch portion (2) is used whose length or diameter is larger than a length or diameter of a die portion (3). The dowel section is required as a guide for a tongue inserted into a buckle and as a load receiver when a latch member is elongated at a time of collision etc. When a ratio C/t of a clearance C between the punch portion and the die portion with respect to a plate thickness t of the buckle base member is set within a range of ?(30 to 5) %, no crack is generated in the root of the dowel section, and the dowel section of a shear cross-section length ?0.25×t, a shear cross-section starting height ?0.7×t, and a height of (0.70 to 0.95)×t is easily obtained, and the perpenducularity of the dowel section side surface is enhanced.

Abstract: When forming a dowel section by performing press working on each of portions constituting side walls of a buckle base member, a die of a negative clearance with a punch portion (2) is used whose length or diameter is larger than a length or diameter of a die portion (3), the dowel section being required as a guide for a tongue inserted into a buckle and as a load receiver when a latch member is elongated at a time of collision etc. When a ratio C/t of a clearance C between the punch portion and the die portion with respect to a plate thickness t of the buckle base member is set within a range of ?(30 to 5)%, no crack is generated in the root of the dowel section, and the dowel section of a shear cross-section length ?0.25×t, a shear cross-section starting height ?0.7×t, and a height of (0.70 to 0.95)×t is easily obtained, and the perpenducularity of the dowel section side surface is enhanced.