Why do you need T slot outlets for 20A split receptable outlets?

Why do you need T slot outlets for 20A split receptable outlets? t slot receptacle HUBBELL HBL5461 AC Receptacle NEMA 6-1520 Female Industrial Grade - Electric Plugs tokcer 88 slot Amperage, Wires, Poles, Cord, Plug, Inlet, Connector, Outlet, Receptacle, Adapter 2 Poles, 6-20 · T-Slot · 6-20 T-Slot · 6-20 T-Slot · 6-20 T-SLot · 6-20

tokcer 88 slot A four year old house had several of the ground pin holes blocked in the outlets by a couple of little brass pieces I couldn't plug a three

twin slot shelving spacing Note: A 20-ampere T-slot receptacle or cord connector may accept a 15-ampere attachment plug of the same voltage rating  T slot receptacle Rated 10 amps---but believe me, as long as the contacts are still tight, it will take 15 amps no problemo! They always