Abstract: A seat belt buckle (24) includes a base (80) that defines a cavity (82) for receiving a pair of tongues (62, 64). A latch plate (100) is supported by the base (80) and is movable between a first position connecting the tongues (62, 64) with the base when the tongues are advanced a fully inserted distance into the cavity (82) and a second position at which the tongues are disconnected from the base. A blocking mechanism (200) has a portion located in a path of movement (P1, P2) of one of the tongues (62, 64). The blocking mechanism (200) is operable to block advancement of the tongues (62, 64) the fully inserted distance into the cavity (82) until both tongues are advanced into the cavity together a predetermined distance. The blocking mechanism (200) comprises a member (204) that is linear moveable relative to the base (80). A pivotable arm (206) carried by the member (204) has opposite end portions (266, 264) which engage the tongues (62, 64).