This finger bump allows for you to always get a perfect 90 degree trigger pull. It can be attached via double sided tape or it can be attached by drilling and tapping a 4-40 NC thread into the side of the chassis. Screws or double sided tape can be provided, just indicate which would be preferred on checkout. 
 
Note: the product pictured is sanded and polished to remove layer lines. If you would like this service we can do this for this specific product but it does come with an additional cost of 20$