NEW YORK — The stock market on Wednesday set another all-time record, and the record, according to the traders describing it, is now being carried by a handful of stocks in a manner that has traders worried, a word traders use when they have not yet found a word with more letters.

The concern is what the math does when you look at it. The S&P 500, the benchmark that 500 companies are contractually required to impress, is at or near its highs. The equal-weighted version of that same index — in which all 500 companies count equally, as if they were all at the same potluck — is down four percent over the past month. The ten largest contributors now account for a record share of the index. Two companies, in analyses circulating on Wall Street this week, are driving roughly a third of the market’s profit growth for the year.

"The average stock is no longer a word a portfolio manager says in a meeting. It is a word a portfolio manager says about a portfolio manager who was let go."

The result is a market that behaves, in the description of one veteran trader, “like a five-person elevator with 495 people waiting in the lobby.” The five go up. The 495 wait. The index, which is what your 401(k) is actually a share of, reports to the press as if all 500 are riding.

“This is not diversification,” the trader said, on the condition of anonymity, which on Wall Street is the condition under which every true statement is made. “This is a group project in which five people did the work and 495 people got the grade. The grade is a record high. The 495 people are in the building. They have been in the building the whole time.”

The diversification angle has produced a small but growing cottage industry of investors who have, in the words of one financial advisor, “technically diversified into five names, which is the minimum the advisor will respect and the maximum the market will let you get away with.” The five names are the names you know. The other 495 are, in the advisor’s words, “a feature, not a bug, of the index, and a bug, not a feature, of your returns.”

THE INDEX, ITEMIZED

  • Constituents: 500. Yes, still 500. The number has not changed. The number is, on the record, doing less and less work.
  • Contributors that matter: Five, by most counts. Ten, by the forgiving counts. The top ten now represent a record share of the index, which is a sentence the S&P has never needed to be true about itself.
  • Equal-weight S&P, past month: Down 4%. The 500-stock version, up. The 5-stock version, up more. The 495-stock version, in the words of one analyst, "the lobby."
  • What the record high means for your 401(k): Your 401(k) is, in the specific, a share of the index. The index is, in the specific, a report card. The report card is, in the specific, an A+ written by five students.

The practical question, the one every advisor is fielding this week, is what happens if the five slow down. “The market is at a record high,” one portfolio manager said. “The five are at a record high. The other 495 are, on the record, watching. And the word ‘watching’ is the word we use for a market that is not, in the specific, participating.”

At press time, a brokerage on the street was preparing to launch a fund called the Other 495, which will invest exclusively in the 495 stocks that are not the five. The prospectus, in its first paragraph, states that the fund’s objective is “to not be the five,” which is, in the specific, the first investment objective in history that is a negation, and the only one that is, on the record, also a prayer.