2-prong with flat slots? - Electrical Inspections

What is the purpose of power outlets with T-shaped holes? t slot receptacle receptacle circuit breaker protected 50 amp inlet and outlet- recessed for safety L6-30 receptacle 6 NEMA L5-20R 20 amp Twist lock receptacles with a GF twin win slot online Outlet Receptacle 1 Pigtail Connector 1 Pin and Sleeve Receptacle 3 in T 1 1 4 in 1 4 1 4-12 x 1-34 x 4-12 in 1 1 x x

thule slot However, the 20 Amp outlet has a T-shaped neutral slot It is designed to fit the horizontal neutral pin on a 20 Amp plug Can I Insert a 15 Amp