I just spoke with Don at the Bird Nest. Here is what he said. Grommet Part # 18912A IS correct for the Squarebirds. That grommet with the big hole in the center mounts under the antenna and allows you to run the antenna cable from the radio through the grommet and into the base of the antenna. As I recall, my '59 has that grommet in place. The other grommet on the firewall, grommet Part # 359451S, is also correct for the Squarebirds. It allows you to run that antenna cable from the radio, out the firewall, to that 18912A grommet. It has several holes in it that also allows you to run the vacuum wiper hose through it, and anything else you might need to run through the firewall. So, yes, both are correct for the Squarebird according to Don.