Huck bolts aren't breakaway per se, but just like threaded bolts, they can be. The difference between Huck bolts and threaded ones is that Huck bolts are fastened by cold swadging a collar on the "threaded" end (which is threaded with annular rather than spiral threads) instead of using a threaded nut. This goes a long way toward preventing their coming loose in service, such as holing drawbar lugs to center sills. One of the most common places you see them is holding the sides to the framing memebers in open top hopper cars.