When ordering a FCG how do you know what FCG to order? I am having  a Polish under-folder built.
Can anyone recomend a builder and what type of receiver to use. Thanks for the help new to building AK's.
                                                                                                          Thanks!!!

                                                                                                          F-R

Single vs double is going to depend upon the receiver you use.  Any receiver that is cut out for a double hook can use either a single or a double hook FCG.  A receiver that is cut out only for a single hook can only use a single hook unless you modify the receiver.  I would suggest a Global 1.0mm receiver for your build.  Globals are cut out for a double hook FCG which means you can either use a single or a double.  All things being equal, I'd get the double hook.