What is a 'Lightening Link'?

[Major Tom]

I heard of this before but was never able to find any info on it. Supposedly fits in an AR15.

[SMOKEY]

Watch the spelling. Google AR15 lightning link. I think that is the spelling

[k arga]

auto sear to convert semi to full auto, needs to have tax stamp.

[Major Tom]

auto sear to convert semi to full auto, needs to have tax stamp.

Oh, OK. So that's what it is!
Thank you

[garandeguy10]

Google Drop in Auto Sear. You need to have a tax stamp on this or you are facing serious Federal and State Charges. Possession of an unregistered Drop in Auto Sear is the same as possessing a unregistered (untaxed) machine gun, even if you do not possess a gun to put it in.

[Major Tom]

I not planning on buying or making one. I was just curious what it was. I have no need of full auto shooting as I did plenty of that in the Army.

[n64atlas]

The drop in auto sear is not the same as the lightning link. They will both give you full auto, but are different construction.
As stated, unless you are a Class 2 with an SOT or bought a NFA registered sear of either type, they are not legal.