Lycoming studs have different threads at either end. One side fits nicely for the associated nut, on the other the nut binds after only one turn or so. This is by design as the binding thread locks the stud in place with its interference fit into the aluminum. No thread locker needed. You’ll also note that the ends of the studs are a different contour showing you which side is to be installed into the aluminum head/case etc.
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