Ah, Stronglight cranks, they do indeed have a non-standard thread so a normal square taper extractor doesn't fit - the only tool for them is made by J A Stein Company. I had to buy one ages ago which you'd be welcome to borrow but I'm abroad indefinitely.
Perhaps email that photo to Spa and they might be able to clarify. Alternatively there may be someone on here who can lend you their tool.
Most helpful! I've dropped them an email to confirm, but ideally i'd like to borrow someone's for beer money, since I'm replacing the stronglight with a Shimano 600 crankset and probably won't need the tool again - will put a post out once i find out exactly what size is needed I guess
Most helpful! I've dropped them an email to confirm, but ideally i'd like to borrow someone's for beer money, since I'm replacing the stronglight with a Shimano 600 crankset and probably won't need the tool again - will put a post out once i find out exactly what size is needed I guess