In 1968, Weber designed a new friction leg socket and filed a patent for it. Beginning with the 1969 model year, these new sockets were put into production. While Weber awaited their patent for these new sockets, they started stamping the top vent with “PAT PENDING”. These new leg sockets eliminated the need for metal thumbscrews. The patent was filed for on November 22, 1968, and it was granted (Patent # 3538906) on November 10th 1970. However, in spite of this the Weber catalogs and literature at the time continued to list the kettles as “PATENT PENDING” through the 1972 model year. The patent number is first listed in the 1973 catalog. There are quite a few examples of these “PAT PENDING” kettles out there. It’s safe to assume any grill with Patent Pending on the vent is a 1969 or 1970 grill however depending on wheel style they could be from as late as 1971-72.