Standard 3-pole breakers are rated for 240 volts. 1-pole and 2-pole are rated 120/240 volts. Only the breakers connected to the high leg need to be rated for 240 volts. As other have said 240 volt 2-pole are available but not often stocked by supply houses. You could use a 3-pole breaker instead of ordering a 2-pole if you have space in the panel.
