The bottom line you mean the part that the preset will screw in to? if so then just screw it into your grip frame, I would suggest that you would be better served using an inline on/off as well or get a combined bottom line attachment with on/off built in such as the Unimount rather than a drop forward. If you don't have some kind of bleed valve system then you run the risk of unscrewing your preset reg from the bottle.