The Yankees will hit another milestone this season besides the retirement of Derek Jeter: It’s the last time a single-digit jersey will be worn by a Bronx Bomber.

When he made his major-league debut on May 29, 1995, Jeter wore No. 2. It was one of only two single digits left for a Yankee, the rest having long since been retired.

“It’s fitting for Derek to have one of the last single-digit numbers that remains,” said then-teammate David Cone in 1999. “I’m not sure if it was intentional, but whoever made that decision, it was a pretty good guess.”

The number was assigned to — not requested by — Jeter, says a team spokesman.

The Yankees first used numbers in 1929, and they were assigned according to batting order. A few years later, some teams correlated numbers with position played, and eventually a looser system took hold league-wide: the higher the number, the lower the status, with single digits reserved for “everyday players.”

Although much lore surrounds the bequeathment of No. 2 on a young Jeter — including a claim that as far back as high school, scouts knew that he was destined for Cooperstown, that he’d be a lifelong Yankee and the greatest shortstop of his generation — the truth is far less glamorous.

“Before Derek Jeter, Number 2 was worn by Mike Gallego [1992-1994], who you’ve never heard of,” says Marty Appel, a former p.r. guy for the Yanks and ­the author of “Pinstripe Empire.”

Jeter’s retirement marks yet another accomplishment in a golden career. He will be the last Yankee to wear a single digit, joining the pantheon of greats who transcended the team to define the game.

Here’s how each of them wound up with their lone numbers.

1 BILLY MARTIN

The boozer and brawler known as “Billy the Kid” began his career as a Yankee with No. 12, but in 1951, No. 1 became available and the second baseman took it. “It was laughingly said [by clubhouse attendant] Pete Sheehy that Number 1 was the only number that worked for the very skinny Billy Martin,” Appel says.

In 1957, after a brawl at the Copacabana involving Martin, Yogi Berra and Mickey Mantle, the Yankees considered him too much of a liability, and he was traded to the Kansas City Athletics.

He was hired as manager by George Steinbrenner in 1975, and throughout his on-again, off-again relationship with the ball club — he was fired and hired five times over the course of 13 years — he always came back as No. 1.

“Nobody bled team colors like Billy Martin,” Appel says. “It always seemed to be available for him — as if they knew he was coming back.”

His number was finally retired in 1986 — though he wore it again when he came back to manage, for the last time, in 1988.

Martin died on Dec. 25, 1989, in a car crash in upstate New York. He was buried in Westchester County less than 200 feet from Babe Ruth with a “1” engraved on his tombstone.

He chronicled his life in an autobiography titled — what else? — “Number One.”

3 BABE RUTH

The Sultan of Swat was infamously sold by the Boston Red Sox in 1919 to the Yanks, but this was before the Yankees had adopted numbers for players. (The Cleveland Indians were the first major-league team to do so, in 1916.) In 1929, when the Yanks first assigned numbers, Ruth was given No. 3 because, as was custom, that was his place in the batting order. (The pinstripes were a Babe-driven addition; management hoped they’d make him look less fat.)

Ruth wore No. 3 from 1929 to 1934 and left the Yankees after they refused to fire manager Joe McCarthy (always numberless) and hire him. The Yankees kept No. 3 in circulation for years after, and it was worn by seven other players until June 13, 1948, when it was retired in a ceremony at Yankee Stadium. The Babe died of throat cancer two months later.

4 LOU GEHRIG

Like Ruth’s, Gehrig’s number reflected his place in the batting order. But No. 4 is distinguished as the first number to ever be retired in all of American sports. The greatest first baseman baseball had ever known — and its most indestructible, playing in 2,130 consecutive games — fell ill in 1938, 15 seasons into his career as a Yankee. On June 18, 1939, he was diagnosed with the degenerative disease ALS.

On July 4 of that year, the Yankees declared “Lou Gehrig Day” and retired his number. The Iron Horse famously told the crowd, “Today, I consider myself the luckiest man on the face of the earth.”

He died almost two years later, on June 2, 1941. He was 37 years old.

All luxury suites at Yankee Stadium are marked by a retired number, with a list of every player who ever wore it — but only one name appears on Suite No. 4.

5 JOE DiMAGGIO

In his rookie year, 1936, Joltin’ Joe — who debuted batting ahead of Gehrig — was first assigned No. 9 by Yankee manager Joe McCarthy. “They knew he was going to be an everyday player,” Appel says. “Almost more than Jeter, they saw him as someone who was going to be a big, big star.” One year later, McCarthy — who loved DiMaggio as a player and a person — assigned him No. 5. According to “A Hero’s Life,” a biography by Richard Ben Cramer, it was clubhouse attendant “Pete Sheehy’s highest tribute: There was the Babe, there was Gehrig . . . and Number 5 was DiMag.”

When DiMaggio enlisted in the Air Force in 1943, the Yankees held No. 5 in reserve, allowing no other player the honor. The Yankee Clipper returned to the field in 1946 and retired on Dec. 11, 1951. His 56-game hitting streak still stands. His number was retired in 1952.

6 JOE TORRE

Not officially a retired number yet, but it’s only a matter of time. “We haven’t given it out for a reason,” GM Brian Cashman said last year. Torre wore No. 6 throughout his legendary tenure as Yankee manager, from 1995 to 2007. Under him, the Yanks made the World Series six times and won four.

“Torre got Number 6 mostly because, like such other stories, it was simply available,” Appel says. “Infielder Tony Fernandez had worn it the year before, but he was no longer on the team. The irony with Joe’s Number 6 is that he wore a jacket so often, many [fans] would say, ‘He wore a number?’ ” (As the Braves’ manager, Torre wore No. 9, the same number he wore when he played for the Cardinals and Mets.)

7 MICKEY MANTLE

In his rookie year, 1951, Mantle was No. 6. “Mickey was a much-touted, 19-year-old rookie,” Appel says. “They really wanted to make sure he followed in succession of numbers, 3, 4 and 5 — Ruth, Gehrig and DiMaggio. He seemed the heir apparent.”

But he had a rough year, and management sent him to the minors. “Bobby Brown, who had been in the service, came back and reclaimed Number 6,” Appel says.

When Mickey was recalled to the majors, he became No. 7 and played another 17 seasons for the Yankees, an All-Star for 16 of them. “Nothing ever seemed as perfect to me as the Number 7 on Mickey’s back,” Appel says. “It’s Lucky Number 7, a bold shape, no circles. Nothing ever seemed as right.” He stopped playing in 1968 but wore the number once more as coach in 1970, even though the Yanks had retired it in 1969.

8 YOGI BERRA, BILL DICKEY

How fitting that Yogi Berra — who famously said, “It ain’t over till it’s over” — had, until last year, the only number in baseball history to be retired twice.

Yogi joined the team in 1946 at No. 38, but by 1948, he was given No. 8. “That recognized that he was special,” Appel says. He wore No. 8 through his next 16 seasons as catcher, until retiring in 1963, and one year as manager in 1964.

Before Yogi, catcher Bill Dickey wore No. 8 through his 13 seasons and again as manager in 1946.

“It’s important to note that Bill Dickey was every bit the player Yogi was,” Appel says. “He was held in such high regard that when Yogi was fresh in everyone’s memory, they did a poll asking, ‘Who was the greatest catcher in Yankees history?’ and the fans said Dickey. When Yogi went into the Hall of Fame in 1972, and they felt it was appropriate to retire the number, they thought, ‘How could we not honor Dickey, too?’ ”

Yogi didn’t return for the ceremony; he was across town, managing the Mets — where he wore No. 8. No one held it against him, and when he came back to coach, then manage, the Yankees (1976-1985), he again wore his trademark number.

9 ROGER MARIS

Maris was traded to the Yanks from the Kansas City Athletics in 1959. He was No. 9 in Kansas City, so he was given No. 9 here. “He didn’t want 9; he was just assigned 9,” Appel says. “Today you find players who like to have numbers they’ve had success with. Sometimes you’ll see a player pay another player thousands to give up his number, but I don’t remember that being the case with the Yankees.”

In 1961, Maris broke Babe Ruth’s home-run record, hitting 61. He played for the Yanks for seven seasons, and the only other player of note to wear No. 9 was Graig Nettles, from 1973 to 1983. No. 9 was retired in Maris’ honor on July 21, 1984. He wore his uniform to the ceremony. He died a little more than a year later, on Dec. 14, 1985, of Hodgkin’s lymphoma.