Difference between front and rear road caliper
Is there any difference between a front and rear shimano 105 brake caliper?
i.e. can I fit the front to the rear?
me have long head tube
Usually the only diff is in the length of the bolt that attaches the caliper to the frame. Front is a longer bolt since it needs to go through the fork. You can use a front caliper on the rear but will need to get a shorter bolt.
However, if you're in need of a rear brake there are lots more widowed rear calipers out there, lots more than widowed front calipers, because lots of people run the front brake only on a fixed gear or singlespeed bike.
Got a box of bits so should be able to adapt it, just wanted to make sure!