i think its usually an 8?
i just need to slide the caliper up to take out the pads and slide new ones inTake the 2 17mm bolts off?
i believe its that. which makes sense because i had two allen wrench's one a size bigger than the other and both was either too small or too big..its a 4 for the rear and a 7 for the front which you wont find in a allen key set, you will have to ask for a brake caliper key. hope this helps.