Dual-threaded shaft w/one-way clutch.

The two threadings are 1.375x24tpi for the bottom portion, and M30x1. These are the threadings for standard freewheels and sprockets and BMX "mini" freewheel.
The ID of the clutch is 20mm.

2009/11/28 13:14:38

Exposure mode: program (auto)
Metering Mode: matrix
Exposure time: 0.0091 s (1/110)
Aperture: f/2.8
Focal length: 8.0mm (35mm equivalent: 37mm)
ISO: 200
Flash: No
File size: 1971223 bytes
Camera maker: FUJIFILM
Camera model: FinePix F10
Resolution: 2848 x 1897