I'm sure he's referring to the tension spring RM.
If the plastic stock is one of the old Combat Exchange/ATI Ultra-lite folding stocks then yes the holes for the tension spring were usually too small a diameter and need to be drilled out to size. Be careful though because the drill bits like to grab that plastic and you'll drill too deep before you know what happened. Another option is to go to a hardware store like ACE and get a spring with similar tension that is the correct diameter for the hole. You can usually get one for a couple of $.
If you picked up an OEM stock and the spring won't go in, sometimes you have to force it as it is made to be a little bit of a tight fit so the spring does not fall out and get lost during a field cleaning. Having said that, yes the hole in an OEM stock can be drilled out as well, but again be careful of the depth.