Faq II: Equipment & Maintenance:

2.9 Guards

     Foil guards vary mostly in diameter, being between 9.5 and 12 cm
     across.  The largest guards (eg. Negrini) may fail the weapon
     guage check if they are dented or misshapen.

     Epee guards are almost always the maximum diameter (13.5 cm) for
     best protection, although they can vary considerably in shape,
     depth (3 - 5.5 cm), weight, and eccentricity (up to 3.5 cm off of
     center).

     "Mini epee" guards are available from some vendors, but they are
     recommended only for Pentathlon.

     Sabre guards come in left- and right-handed versions (the outside
     of the guard being larger).