⌀  
 Diameter Sign
Unicode: U+2300
HTML: ⌀
About this Symbol
The Diameter Sign symbol (⌀) is a Unicode character with code point U+2300. It belongs to the Programming Symbols category of Unicode symbols.
Usage Examples
- Plain text: 
⌀ - HTML: 
⌀ - Unicode: 
U+2300 
How to Type
Windows
Hold Alt and type 8960 on the numeric keypad.
macOS
Press Command + Control + Space to open the Character Viewer, then search for "Diameter Sign".