The vent liner is your flash hole. Its made out of 17-4 SS which is far better than 416ss for this application. When the hole grows too large you just replace the vent liner. Its about $5-$6 vs buying a whole new breach plug. Get a 1/8" hex head drill bit too. You will want one to clean out carbon in the flash CHANNEL. The flash hole or vent liner in the case of the Lehigh plug is also closer to the primer. You will get a bit more heat to the powder.