Modding contacts on 300/4D for teleconverter

but the lower pressure gasoline in 22:1 or better diesel can be catastrophic.

Not necessarily - if it is an older model without direct injection or common rail and the amount is small. In older diesels it was a common trick in winter to add a few liters of gasoline to the diesel tank (though it should be unnecessary with winter diesel). Naturally, a full tank of gasoline spells death for the diesel engine and the entire fuel system. An inattentive gas station attendant did that once on my dad's Mercedes diesel - and fortunately realized the mistake before my dad started the engine - all it took was to pump the gasoline out of the tank and put the correct diesel in there. Had he started the engine things would have been a lot more expensive and inconvenient. At least in Germany it is still possible to insert the wrong nozzle into the filler neck on a variety of cars.

Yes. The UK system I believe is the same as the US - the diesel nozzle is bigger, and doesn't fit in the petrol/gas tank's hole. Unfortunately I was encouraged to go to an unfamiliar fuel station by my wife (who nagged me to use a voucher), and since my normal fuel station offers normal and premium versions of both petrol and diesel, I allowed myself to get confused by the premium petrol hose next to the diesel hose. The nozzle was loose, but I was at an awkward angle due to the hose position, and again it was a new fuel station with different hose colouring from what I was used to. I was exhausted, and the only reason I filled up was that my wife was taking the car for a service the next day. She got part way there when the engine died. Fortunately it seems to have survived with only a new filter, although I gather it might have killed the fuel pump, and diesel engines rely on the diesel fuel for some lubrication (according to the mechanic). Which is odd, because I thought diesel engines could be made to run on chip fat, among other things, so I wasn't expecting them to be tricky. All in all, expensive, but it could have been worse. Live and learn.

Still, if you have two nozzle and two holes to stick them into, and the intent is to stop incorrect nozzles going into incorrect holes, anyone with a toddler should have thought to change the shape rather than the size. Make one a square and one a circle, and there wouldn't have been a problem. It's almost like car manufacturers like being paid lots of money to strip down the engine...

I do wonder whether a bayonet fitting is really the right way to do a camera mount anyway. The number of times I've struggled because I'm trying to mount the camera on the lens rather than the other way around, or the tripod foot fouls on the hand grip, or something clouts the prism... It feels like some kind of latching chamfered push-in arrangement would have been more me idiot proof and less prone to rubbing bits of lens on delicate bits of body. Again, I guess we might see when something mirrorless turns up.