I'm sure a lot of people out there know this, but I just found out today and figured it could help someone. It turns out the post o-rings on a ball lock keg are #9 which you can pick up a pack of 10 at one of the box stores for under $3.
Backstory. I've been acquiring equipment to start kegging. Got my kegs, new set of o-rings, and all that jazz. After putting the new o-rings on the posts, putting the gas disconnect on, and pressurizing, I heard a hissing sound... Never good. I put the old o-ring on and the sound went away. Maybe the new ones are cheap or poor quality control, who knows. But went to the plumbing section at Lowes and found some that seemed like the right size and sure enough, they are.
Take it for what it's worth, but it worked for me!
Backstory. I've been acquiring equipment to start kegging. Got my kegs, new set of o-rings, and all that jazz. After putting the new o-rings on the posts, putting the gas disconnect on, and pressurizing, I heard a hissing sound... Never good. I put the old o-ring on and the sound went away. Maybe the new ones are cheap or poor quality control, who knows. But went to the plumbing section at Lowes and found some that seemed like the right size and sure enough, they are.
Take it for what it's worth, but it worked for me!