A fail-to-deliver happens when a seller does not deliver shares by the settlement date. The SEC publishes the outstanding fails for every security twice a month, with a delay of roughly two weeks. Large or persistent fails can come from short selling, ETF creation and redemption, or operational problems.
Under Regulation SHO, a security with fails of at least 10,000 shares and 0.5% of shares outstanding for five consecutive settlement days goes on the exchange threshold list. This page estimates those streaks from the SEC data; the official lists are published by the exchanges.
Compiled from public SEC EDGAR data. Times are US Eastern. Titles link to the original filing on sec.gov. Information only — not investment advice. Updated: