Hock Backing Iron 50.8mm 2"" (suits Stanley #4 & #5 Planes) BK200
To maximize your plane's performance, a thicker chip breaker (cap iron, backing iron) can stabilize the blade's cutting edge reducing vibration and chatter.
HOCK Chip Breakers or Backing Irons are 3mm thick (.118"), almost twice as thick as a stock chip breaker.