Stock lug NUTS (not "lugs" -- technically, lugs were bolts with tapered seats that screwed into the hubs to hold the wheels on. That's the way it was done up until the mid- to late 50s but most of you grasshoppers probably never saw a car with genuine "lugs") take a 3/4" socket. Most after-market lug nuts in 1/2 x 20 use a 13/16 socket.
The stock lug nuts, as Mike alluded to, have a very thin stainless steel cap crimped on over an open core. If the cap has fallen off, a 19mm socket is just a teensie bit smaller and may work if the 3/4" doesn't.