Hobbico Cup Screw O-Ring DA500Tower Stock# LR0644 • Manufacturer Stock# HCAR4331
It is located inside of the Color Cup and under the Cup Fixing Screw.
One Color Cup Screw O-ring (key #31)
None, item is a stock replacment part.
Outer diameter: 9mm (.354")
If the Color Cup Fixing Screw is needed, use HCAR4330.