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Just pick up a 7x1.0 bleed nipple from a motorfactors, you have a spare unit to try and screw it into- you could even take it with you to the shop!
It looks like 7x1.0 to me from your photo if the others are 10x1 and 8x1.25.
Typing 7x1.0 into eBay it seems they fit a Clio as well as most motorcycles.
Get ordinary plated steel, not stainless, they will just seize into the cast iron.
If it suddenly breaks, go back to the last thing that you did before it broke and start looking there