Billiard Tips
Billiard Tips reside at the end of a pool cue stick and are used to strike the ball directly. Leather tips of varying curvature and degrees of hardness are glued to (or in some cases screwed into) the ferrule. The de facto standard curvatures for a pool tip are dime- and nickel-radius, determined by shaping a tip so that when one puts a nickel or dime to it, they have the same curvature.
The Billiard Tip end of the cue will vary in diameter but is typically in the 10 to 14 millimeter range with 12–13 mm for pool cues, and 10–11 mm for Snooker cues being most common. Rounder (i.e., smaller radius) tips impart spin to the cue ball more easily since the point of contact between the tip and the ball requires less distance from the center hit imparting the same amount of spin, due to the increased tangential contact.
Tips for break and jump cues are usually nickel radius or even flatter, and sometimes made of harder materials such as phenolic resin. The shots are more forceful, and usually require less spin. You always want a Billiard Tip to be in good condition.