Are you having some communication issues with your horse?  Head flipping?  Your left and your right a “bit” wonky?  Check out these resources on bits.

Horse Channel’s Online Bit Guide
Source document: http://www.horsechannel.com/horse-exclusives/online-bit-guide.aspx

Bitology from Weaver Leather
Source document: http://www.horsechannel.com/horse-exclusives/online-bit-guide.aspx

Choosing a Bit 
Source document: http://www.equisearch.com/article/tmarticle5

How to Choose a Bit for your Horse 
Source document:http://horses.about.com/od/bitsexplained/a/choosingabit.htm

And Wiki How breaks it down to laymans terms right here.