Historical clue formulations

• Parts of a story structure? — 2026-03-21
• Skyscraper's skeleton, often — 2026-03-18
• Construction materials named after a capital? — 2024-02-17
• Letter-shaped building girders — 2021-05-11
• Letter-shaped girders — 2018-01-01
• Building supports — 2016-12-10
• Metal supports in skyscrapers — 2011-09-27
• Girders — 2006-04-19
• Structural members — 2004-07-28
• Steel supports — 2003-10-08
• Support group? — 2001-11-23