John, I had a batch of parts laser cut by https://fractory.com/ I had various different parts cut including wheel speed trigger wheels for both front and rear wheel speeds, and a few other unrelated parts, all cut from the same sheet of 1.5mm mild steel sheet. Most of the cost is actually in putting a sheet of steel on the machine. If I'd just wanted two parts, the cost would have been about £85 inc delivery. I ended up having 25 parts cut in total for just under £90 delivered. The trigger wheels I had cut all have sixteen teeth, and have an OD of around 104mm once folded (each tooth is folded and the sensor mounted at 90° to the shaft). The rear wheel speed trigger wheels are actually designed to be mounted on the inner end of the drive shaft, with sensors mounted on brackets off the side of the diff. The sensors I'm using have a sensing range of 2.5mm, so are much less sensitive to adjustment to those that Caterham supply, so much less susceptible to mechanical damage through being set too close to their target, or not seeing the target by being too far from the target (maybe due to a flexing bracket?). https://uk.rs-online.com/web/p/proximity-sensors/1646098/?relevancy-data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searchHistory=%7B%22enabled%22%3Atrue%7D