San Francisco-based apparel retailer Gap Inc. will literally ring in its 40th anniversary, by sounding the closing bell at the New York Stock Exchange this Friday.

As part of the celebration, Gap is also outfitting the Exchange trading floor on Friday. It marks the first time in the Exchange’s history traders will dress down for business and wear the retailer’s brand new 1969 Premium Jeans, launched this week, to work. Later at 4 p.m., Gap Brand President Marka Hansen and founding family members will ring in the closing bell remotely from their West Coast headquarters.

The retailer also plans to host the largest simultaneous acoustic concert across 700 stores in the U.S., with 700 performing musicians, this evening. The in-store parties are scheduled to take place from 7 -9 pm and offer customers $20 off their favorite jeans and an additional 15% of their entire purchase.

Gap Inc. operates more than 3,100 stores in the U.S., U.K. Canada, France, Japan and Ireland, with franchise agreements in Asia, Europe, Latin America and the Middle East. Fiscal 2008 sales for the company, whose brands include Gap, Banana Republic, Old Navy, Piperlime and Athleta were $14.5 billion.