TriVelox's first design was an entertainingly brutal, deliciously steampunk, device.

The chainline remains straight in all gears, so the gear is changed by moving the sprocket cluster sideways. The sprocket cluster slides on a set of splines on the outside of the tubular body that contains the freewheel ratchet.

The gear change mechanism is a shaped plate that sits between two of the sprockets. The gear lever pulls a cable, and this cable then pulls the shaped plate sideways. You can see some explanation of all this in this TriVelox brochure.

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This example has had relatively little use. Its features include:

• It has a fairly short cable adjuster.
• The main arm is reasonably well finished with well rounded edges.

Note that the TriVelox brochure states that the force to change to low gears comes from the two telescopic springs surrounding the sliding rods. Both of the derailleurs that I have also have a conventional, and rather more purposeful, helical spring around the cable.

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• Derailleur brands: TriVelox
• Country: UK
• Date of introduction: 1934?
• Date of this example: unknown
• Model no.: unknown
• Weight: 438g excluding chain tensioning spring
• Maximum cog: 26 teeth? - this is the biggest sprocket offered by TriVelox
• Total capacity: 24 teeth? - a guess based on the range offered by TriVelox
• Pulley centre to centre: 78mm
• Index compatibility: friction
• Chain width: 1/8"
• Logic: low normal
• B pivot: none
• P pivot: sprung
• Materials: steel