You mean the push in wire connectors on the back of the real cheap receptacles? Throw those things away. The NEC only allows 14 gauge wire, max to be used in the push ins.
Best receptacles to use are Leviton Pro Grade, or a comparable Cooper/Eagle or Hubbell, all of which will have holes in the back you put wire in, and tighten screws down to clamp the wires between serrated plates in the receptacles. Very good quality. Leviton even has a nylon face plate version, distinguishable by its absolutely flat face around the slots. Look thru the slots on any of these I mention, and you will see the innards of a 20 amp rated receptacle even in the 15 amp only version.
Charles