Some metal tweezers have a spike in one arm and a corresponding hole in the other. When closed, the spike goes through the hole and pokes you in the thumb. What’s the purpose of this? It’s annoying, and the only reason I can think of is to prevent you from squeezing too hard.
I think it’s to keep the jaws aligned.
good reason, it lets you know the amount of force being applied to the jaws so you don’t crush something delicate.
It’s an indexing rod and hole, to keep the jaws aligned.
I’ve had some cheap-o-matic brands that didn’t have that feature, the *#&@$! jaws would slip sideways and drop whatever I was holding, typically a precious stone.
It was so annoying, I immediately tossed that junk and got GOOD forceps.
I use tweezers/forceps on a daily basis on the job*, and they work just fine without the “spike”, which is useless to me at best.
*for picking up and transferring bits of delicate tissue for pathology applications.
I thought that due to the thickness of the arms, they’d be resistant to sliding past each other (in the way that the spike would prevent). I guess it’s more useful when holding hard and rounded items, like gemstones. I only use them to pick up squishy objects, so I guess that’s why I never found out how useful they are.