Panasonic TY-EW3D2MU 3D Active Shutter Eyewear for Panasonic 3D HDTVs - Medium Small = 19"-21" head circumfrance; Medium=21"-24" head circumfrance; Large=24"-27" head circumfrance Easy to operate slide switch 3 sizes available to suit your needs (S, M, L) World's lightest pair at approximately 39g Rechargable battery for repeated use World's lightest pair at approximately 39g 3 sizes available to suit your needs (S, M, L) Rechargable battery for repeated use Easy to operate slide switch Small = 19"-21" head circumfrance; Medium=21"-24" head circumfrance; Large=24"-27" head circumfrance