If the Shimano Positron AX was the coming together of Shimano’s disastrous Positron technology with its much sneered at AX aerodynamic design. Then this derailleur was Bridgestone and SunTour’s riposte - the coming together of Bridgestone's widely ignored in-derailleur indexing technology, with SunTour's derided Trimec design and hopelessly unreliable ‘Tech’ three pivot technology.

And just like the Positron AX, the result of this marriage of monstrosities was a surprisingly solid and workable derailleur. Albeit one that nobody wanted to buy.

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This is a later, black, example with a medium length, openable, pulley cage. It has an 'improved' second pivot seal which is clearly branded SunTour but which I have not seen fitted on a SunTour derailleur

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• Derailleur brands: Bridgestone, manufactured by SunTour
• Themes: Indexing insanity
• Country: Japan
• Date of introduction: 1984?
• Date of this example: 1984 (two letter date code is AI)
• Model no.: unknown
• Weight: 405g
• Maximum cog: 28 teeth?
• Total capacity: 28 teeth?
• Pulley centre to centre: 65mm
• Index compatibility: 5 speed?
• Chain width: 3/32”
• Logic: top normal
• B pivot: unsprung
• P pivot: double pivot, both sprung
• Materials: largely steel with aluminium knuckles