As other people have noted it's a pump peg for a full size frame pump.

You want a full size frame pump because it will get 700x25mm road tires up to riding pressure in 90 strokes. Unlike CO2 cartridges, it can't run out if you help another rider who flatted or get a slow leak you can't find from a piece of tire wire.

You can use a short strap to keep it from rattling or falling off on a humongous bump.