Chainring bolts, or knees.
Knees is the most likely answer so far. It's a spiderless crank, and the locking was loctited on at approximately BastardTight™️ Nm
Chainring bolts
I was going to say this.
If it's direct mount then the interface between the ring(s) and crank arm.
@Five-Hats started
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Chainring bolts, or knees.