The checkering pattern on the Arisaka safety was machined, apparently in a two-pass operation. The lines on the side would have been put on by forcing the part through a die. That was done while the part was "in the white" and soft; it would be hardened and rust blued later.
All that work was eliminated in the late-war rifles, where the weld that joined the knob and the spindle was left as it was and the safety knob was not checkered.
Jim
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