NOSTALGIA ALERT!
Those of a certain age, may have memories of an entertainment programme called "wheel tappers and shunters club"
Railways employed men with a hammer to "ding" a railway-wheel...the sound would alert to any that were unsound.
I suspect the screw-thread on the head is primarily to overcome the differential-expansion problem, while the engine temperature stabilises. Not enough attention is given to proper warming and heat-soak.