Yes, apologies, I slightly misread your earlier post.
I think I'm still right, though!
The friction between the disc and the hub you speak of, this itself is generated by the clamping effect of the screws, I agree. But by that argument, you could say that "all" bolts are tension, rather than shear. Structurally, bolts like this are normally designed in shear, according to all the design codes I know, with the exception of certain particular High Strength Friction Grip type bolts with oversize hexagon heads to generate the assumed design clamping force. Cap head allen screws would certainly not normally be designed by the "clamping " method.
But hey, this all getting a bit too much like work!
I'm supposed to be on my lunch-break!
[Edited on 18-3-2005 by moto748]