Adjustable rate of fire controllers

[ps]

http://www.youtube.com/watch?v=jkWAzQiYppo&eurl

Any idea on how this is achieved?  This is what I've been longing for.  Except used with the triggers.  If anyone has any tips on achieving this, please share!  Thank you.

[Modded Matt]

as he stated this is very simialr to the 3 & 4 mode rapid fire kits at the shop on this site. the fire rates here have been perfected for the different games that are commonly used, so you dont have to togglew between 50 different speeds to get to the one you want. the kits you get from here are on the triggers and not an external button also