Cone
Most common version, usually seen on sailors, fishermen, and soldiers.
Skullcap
The smallest, cheapest version, almost always blue. Found on dockworkers, laborers, and drunks.
Brimmed
Brimmed thrum caps are primarily seen on middle class women and usually red or black.
Round
Round thrum caps show up on market vendors and ice skaters.
Beret
The flatter version of thrum cap, relatively rare. Seen only at parties.
Fez
Short-thrummed caps, less weather-proof but more fashionable and practical.
Bruegel
A brimmed cone, seen in several Bruegel paintings.