This twist-lock 30-amp part is probably the most common type of single-phase three-pole outlets found in most portable generators over 4,000 watt.
Theoretically, its maximum rating is 250Vx30A= 7,500 VA. Practically, since the generator normally provides only 240V and because UL and NEC® 2014 require ampacity derating to 80%, you can get up to 240x30x0.8= 5,760 VA continuously if you balance electrial loads on both 120V lines. The mating plug part number is L14-30P. When you connect a cord to the plug, hook up red and black leads to X and Y, white to the neutral and green to the ground (refer to the wiring diagram above). Use a heavy-duty UL-rated cable suitable for outdoor with conductor gauges of #10 AWG. If you want to assemble a generator cord to temporarily power your house in case of an emergency, see this page for information on dryer outlets.