TIM O'CONNOR WAS a merchant mariner pondering a career change when a warning from his prospective mother-in-law - "You're not marrying my daughter if you continue to go to sea!" - made up his mind.

"I was ready to quit anyway. I got tired of it," O'Connor said. "An old salt told me, when every port starts to look the same it's time to quit. And that was happening."

So he bought a flag company. He knew a bit about flags from sailing, like which to fly when and how to stitch repairs. And as a frustrated artist, he saw endless opportunities for creativity in his new work.

That was 36 years ago. Now, his Humphrys Flag Company in Old City is not only one of the nation's oldest custom flag manufacturers (founded in 1864 by two brothers with the surname Humphrys) - it's also one of the region's busiest.

Think of a flag anywhere around, and chances are, Humphrys made it.

In an industry whose sales have sagged since 9/11 patriotism produced a flag frenzy, Humphrys stays on top of its competitors with its artistry (they're known for their handmade applique work), commitment to country (100 percent American-made) and attention to vexillologic accuracy (vexillology is the study of flags), according to Matt O'Connor, the owner's son and Humphrys' chief operating officer.

And it doesn't hurt, the younger O'Connor said, that Humphrys has "the best headquarters location for any business in any industry in the world" - right across the street from Betsy Ross' house on Arch Street near 3rd.

Tourists "walking around this area tend to be all fired up about flags," Matt O'Connor said.

Inside Humphrys, flags of every color and cause greet visitors, who can buy items or just browse a collection that includes everything from a tattered old double-medallion American flag from 1862 to eye-catching banners featuring zebras (Tim O'Connor's current passion) made by the owner himself.

Not on display is the flag that landed Humphrys in the Guinness Book of World Records. Humphrys seamstresses in 1992 made the World's Largest Flag - an American flag that weighed two tons and stretched 500 feet long and 255 feet wide - for a client. It held the record for 10 years.

O'Connor, who lives with wife Barbara in Chester County near Humphrys' Pottstown factory, will turn 65 next month. But he has no plans to retire.

"It's still fun every day. I love going to work," he said.

On Twitter: @DanaDiFilippo