My chair has gone through several configurations, but I think I am quite happy with it now
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Remove the leg bolts and replacing them with 6mm studs through 16mm ali tube.
Bolt cut up accessory arms to munson rings (brass rings used to suspend pipes from ceilings) and then fit the munson ring to the leg.
Drill accessory arm bolt to the chair using a plywood plate as a fixing plate...... I can't explain that one
The mrs is away at the mo' and she has the camera, when she gets back I will take some piccies to show you what I have done.
28mm munson rings are about 60p each from any plumbers merchant and accessory arms can be had of ebay at about £7.25 for four (inc p&p).