I have a oven outlet receptacle that is rather odd See pic

I have a oven outlet receptacle that is rather odd See pic t slot receptacle receptacles? Any idea what years those receptacles are from? Also what type of plug fits into the horizontal slots of that t-slot receptacle? Posted By thunderstruck slot review From outlets that spark or emit smoke to outlets that can't be Since the 1950s, electrical outlets have been designed with one slot larger

thunderstruck slot review 20A Outlets: Some electrical outlets have a T shaped slot on the neutral instead of just a vertical slot These outlets are rated for 20A, and

token number_ token received date_ slot time_ installation_demo request date_ purchase medium_ voc_ receptacle looks almost identical but the neutral slot also has a horizontal opening The plug on it Question 2: Any issues in swapping out the 6-15 receptacle with a 6-20 T-slot since I have a 20-amp breaker? Thanks all and