This Pollack 4 Pole Heavy Duty Trailer Plug with Cable Guard. (the coiled spring that prevent cable from kinking at the backside of the plug)

• Extended connector body conceals terminals.
• Coiled spring guard keeps cable from kinking
• Unique cable clamp prevents chafing - gives more cable support.
• Dust and water resistant.
• Polarized for proper connection
• Terminals accept up to #12 gauge wire.
• Integral finger grips allow for easy connector removal
• Rated for 12-24 V and 35 Amps.
• Note: plug has a larger pin to accommodate the 35 Amp rating and it will not work with a standard 4 way 20 Amp receptacles.
• This plug matches up with P/N: 37644