Mathematical Double-Struck Capital F 𝔽

Visual Description: The symbol is a bold F formed in a double-struck style, like blackboard bold. It shows two vertical lines and a curved arm, with extra weight along the stem. The overall shape remains readable at small sizes and in digital fonts. It stands out on a page or screen.

Meaning & Usage: The symbol marks a special class of objects in math. It often denotes sets, elements, or structures with a double struck style. In notes and textbooks, it helps distinguish these items from ordinary letters. In software and on calculators, it can label constants or functions so users recognize them quickly.

Historical Background: The double struck style grew from a practical need to distinguish certain symbols on plain paper and chalkboards. Authors adopted extra strokes to separate special letters from ordinary ones. The idea spread with the rise of set theory and algebra, and later digital fonts imitated the look.

Practical Use: In classrooms and notes, the double struck F helps readers identify a class of objects quickly. In formulas, it marks a special kind of variable or constant. In calculators and math editors, you may see it as a quick label for a function. UI controls can group similar items.

See our category page for related symbols.

Look‑alikes: F (U+46).

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