While not a common question, a customer recently asked for the diameter of a Sanwa JLF shaft cover.
The shaft cover is the cylindrical portion of a shaft and dustcover set, an accessory part of most Japanese model joysticks. It protects the metal shaft from most elements, as does the dustwasher protect against dust particles getting into the lever's pivot.
The shaft cover diameter is 8.86 millimeters or .348 inches, when measured with a digital caliper.
The black dustwasher - most common with the Sanwa JLF-CD Shaft & Dustwasher Set is 38 millimeters or 1.49 inches.