The Keen Kutter block plane has 1/4"-20 threads this knob has a hex recess to accept a bolt head. The recess is slightly tapered, so a press fit might work for you depending on the tuning of your printer. If it is loose, or for extra security a bit of glue will hold it just fine.
The top is slightly cupped, so print it with that side facing up. Supports are not necessary the hex recess should bridge easily.
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