How to install Drop In Auto Sear

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Hello:

I'm reside outside of the U.S and we have a problem with a proyect with a AR15 type rifle.

We have the parts to convert to M16 (Trigger, Disconector........) and a DIAS (we have Full Auto guns permised and DIAS are legaly in our contry)

But we don't know how to proceed to install the DIAS, first will be the DIAS or first we install the parts (trigger, fire selector....)???

All request will be for help in our proyect

Thanks for all!