I have a T10 but does not seem snug enough and I do not want to **** up!

A T15's definitely too big, I've used a T10 before, they shouldn't be that tight anyway.

I don't know but it's bloody annoying. I've bled older hopes in a campsite before now but the use of a tiny torx bolt that doesn't appear on my multi tool means i wont be doing that in future.

I don't get this Torx thing. In theory you can get more torque through it and have less chance of rounding off the bolt. However, all the torx tools i've had are crap and the 'point's of the star bend or wear off so you still end up rounding off the bolts.

TX10, and yes, i've had a couple snap off too.

Same size screw as older hope I think – so replace 'em for allen bolts if they annoy you?