The speaker itself is 3.81m (1.5") in diameter and is perfect for any project where you need an 8Ω impedance, and are using 0.25W of power. The speakers are rated at 0.25W, with a maximum input of 0.5W (printed wattage on back of speaker may have either value).

Being originally designed for talking greeting cards, the  speaker is extremely light weight!

This version of the speaker is not designed for use with breadboards.  For that version see here