What kind of plug is this?
You are looking at a International Electrotechnical Commission (IEC) Pin and Sleeve Device.
IEC devices are manufactured by a variety of brands, and are designed to be interchangeable throughout this rock called Earth.
The particular one pictured is a 3 pole 4 wire grounding device, possibly 250/125 volt 100 Amperes, single phase, 3 wire. In non-technical terms, two hot conductors, a grounded circuit conductor (neutral) and ground pin. Very common in North America.
IEC Pin and Sleeve Devices are differentiated by diameter for amperage, color for voltage class, and the clock position of the grounding (or earth) pin.