Tapping a thread in fibreglass?

[William_H]

I would be wary of using "self tapping" type screws including the coach bolts and threaded inswerts. Self tapping is a destructive thread cutting more suitable to wood . I think using a tap which cuts a thread far better in GRP. So ideally the inserts pictured but with a proper thread that you cut with a tap. Epoxy the insert in.
ol'will

 

[Rhylsailer99]

put ptfe tape around the thread use epoxy filler into the threads and the hole then a day later it will screw out leaving an imprint of the thread.

 

[emnick]

Thank you for all the ideas

 

[LONG_KEELER]

I wish I had inspected the outer bearing or spigot on a past boat more often.

When the two studs were withdrawn , only around 30% of the stud width remained . I assume lost to crevice corrosion.