Falling into the category of strong snaffle bits is the double snaffle.  This type of bit has two sets of jointed arms attached to a single ring on each side, with either both joints close to the center or offset from each other (in which case it is sometimes called a Y  or W mouth).   These bits are often manufactured to be even stronger by being made of thin, twisted wire.  Needless to say, the effect is quite harsh on the mouth of the horse.  Because there are two sets of arms, there is significant potential for pinching of the tongue and lips, which causes bruising and thus only creates more resistance or a dead mouth, neither outcome being fruitful for the ultimate goal of using any bit, namely communication.  For this reason, these bits are not recommended for any reason.