Cavalier clutch bleed screw size

I’ve read everywhere it is supposed to be 8mm. Looked bigger than that to me, but I couldn’t check it with my ratchet set because of the nipple sticking out kept it from getting onto the bolt. Planned on using my adjustable wrench but kept slipping off so went to buy a new wrench just for this one thing - figured I would get a 8mm and 10mm just in case - neither one fit. 8 is too small 10 is too big. Cannot find this information anywhere. Did have the clutch kit replaced from the original a few years ago and I supposed it could be different or SAE but don’t want to keep buying new tools. Need to get this job done today.

2001 cavalier 5-speed manual 2.2

3/8 ths English seems to be a very good bet. Converted it would be about 9.5mm As a 17 year old car, the caliper may have been replaced by a re-built one with an English bleeder.

Use penetrating oil and crack the fitting free with a 6 point socket being very careful to support the head of the socket wrench. These are VERY easy to break off!