The Collar Rule, under NYSE Rule 80A, requires that if the DJIA moves up or down two percent from the previous closing value, program trading orders to buy or sell the Standard & Poor’s 500 stocks as part of index arbitrage strategies must be entered with directions to have the orders executed in a manner that stabilizes share prices. The collar restrictions are lifted if the DJIA returns to or within one percent of its previous closing value.
The 2% collar rule threshold is set by the NYSE at a point level that is calculated at the beginning of each quarter. For example, on April 1, 2007, the average value for the DJIA for the preceding month (March 2007) was used to calculate a point level (rounded to the nearest 10 points). This resulted in the 2% collar rule threshold being set at 180 points.