
Things started with an innocent question about slipping the back off a Twelve to regulate a movement and whether in my experience the six visible caseheads were practical rather than simply decorative?
My first reaction was that I knew them to be practical because I had a memory of buying a set of torx headed screwdriver bits from EBay in order to remove a screwed caseback to regulate a movement. But wait a mo, was it actually a Twelve or was it a different watch?

So the first watch to hand was my Twelve X Ti and, lo and behold, a fully threaded caseback with TWELVE flats around the circumference: not a tiny screw in sight.
I should say that I like to regulate my watches and keep all the records in a notebook where I found details of taking recent delivery of my Twelve Nebula (ex EBay) and noting that what I'd done was demagnetise the watch to bring it back into COSC so though the case back hadn't been removed it is held down by six hex headed screws. The "other" watch is a C63 Sealander Elite which does have six torx head screws. You know when "happy ever after" ought to be enough and yet you keep digging?

What I gleaned via google is that (1) torx heads are recommended for applications where higher torque loading is a requirement, (2) hex/allen screws come in metric and imperial and torx sizes are specific.
I can't bring myself to think of a watch caseback as being a high torque application and certainly my experience across two different CW models is that the screws are little more than finger tight.
So how come the C63 Sealander Elite has torx heads and yet the Twelve has hex heads?