P_11.3.740: I've a neat OBJ drop/tower bolt, with the slide+turn rod/bolt carefully extracted from case.

I load case (0.05%), position and parent to swinging door, copying bends from parent. It stays attached when I swing door.

I load bolt, adjust its xyzOrigins to axial to allow slide/turn dials, position in case. Parent to case, it either flies off across scene, or mutates, or both...

Tried parenting to case (parented to door.)...

Tried parenting directly to door....

Worse, using edit to undo wonky parenting did not work reliably. I'd sometimes be left with a misplaced mutant. So, delete and try with duplicate...

Drove me to distraction in a scene I was building. So tried in a much simpler test-scene with flattened box as door, cylinder as post...

Am I missing something really, really obvious ??