8g has a 3/16" back flare. 6g has a 1/4" back flare and a 3/8" diameter front. 4g has a 7mm back flare. 2g has a 5/16" back flare. 0g has a 3/8" back flare. 00g has a 7/16" back flare and a 5/8" diameter front. 7/16" has a 1/2" back flare and a 3/4" diameter front. 1/2" has a 9/16" back flare and a 3/4" diameter front. 9/16" has a 5/8" back flare and a 13/16" diameter front. 3/4" has a 13/16" back flare.