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Why are they particularly used for sram brakes and can I run my sram brakes without them?
They allow the caliper to align squarely with the rotor. If you remove them, you will need to add some washers or something between the caliper and mount to space the caliper out enough to stop it fouling the rotor. As long as the pads are contacting the rotor correctly and the caliper isn't rubbing, the conical washers don't matter.
Depends which ones you're talking about, old SRAM brakes had CPS washers which gave you additional alignment options. Some brake adapters which are wedge shaped require these washers so the bolt sits square.
This one just keeps cropping up, if your adapters are bolt through types with no threads you're stuck with the conical washers, especially if it's got them under and above the calipers, if it's just got conical washers on top, you can change adapter style to a threaded 4 hole type like Hope ones and lose the washers.