Cap Irons (Chip Breakers, Back Irons, etc.) for Traditional Stanley Planes. To maximize your plane's performance, a thicker chip breaker (cap iron) can stabilize the blade's cutting edge reducing vibration and chatter. Set your breaker very close to the cutting edge to best prevent tear-out. HOCK Chip Breakers are 3mm thick (.118"), almost twice as thick as a stock chip breaker. A knurled cap screw is included.