Abstract: A buckle for a seat belt of a motor vehicle includes a lockbar 18 engagable in an aperture 26 in a latch plate 24, which is inserted into the buckle. A slider 16 connected with the lockbar 18 is retained under a lockpin 12 to prevent the lockbar 18 from disengaging the aperture 26 in the latch plate 24, except when a release button 20 is depressed. The surface of the lockpin 12 confronting the slider 16, when the lockbar 18 is engaged in an aperture 26 in a latch plate 24, is provided with one or more protuberances 28 such that when under high load the lockpin 12 becomes embedded in the slider 16 to prevent the slider 16. from sliding with respect to the lockpin 12 and inadvertently releasing the latch plate 24 from the buckle.