Parts of some area calculations

• They're on the thumb side
• Arm bones
• Bike spokes, geometrically
• Some lines in circles
• Variables in (pi)r^2 and 2(pi)r
• Lines from the center
• R's, in math
• Arm stiffeners
• Broadcaster cut international lines

Wiktionary Word definitions in Wiktionary
n. (plural of radius English)