They are 10mm. Here is the site where i saw them-have a look. One is a TTE but i do not know what that stands for.
http://www.vehicle-wiring-products.eu/VWP-onlinestore/brakepipe/brakes.php
Its something I keep meaning to add to my tool box. I was gutted as just after I moved in with my now wife her mother gave away half a garage load of pro quality tools to the young guy that serviced her car including a real heavy duty brake pipe flaring set. They belonged to her late husband who'd been into his cars and I guess she hadn't realised how much I was into cars (despite the fact I'd stuck a dismantled spitfire into the corner of her garage!)
That's the Clarke one, sold under loads of different names. I've got one of those and it's crap.
Why does the pipe have to be filed/chamfered (to approx 30 degrees) before flaring?
I`ve not heard of silicon brake fluid (did you mean synthetic?). Not sure which threads you are referring to on the tool, unless you mean the threads that wind the clamp down that holds the die?