Double Pole, Double Thrown footswitch with latching action.
A shorter throw and less clunk than normal 3PDT footswitches.
See second image for details of how to place the hardware on the switch. There should be a nut at the bottom with a split washer above. These go inside your enclosure. The solid washer and another nut go on the outside. Without that inner nut there's a good chance you'll pull the switch out of its housing when tightening.