I really think it depends on the manufactor. My Colt had no way to do it, it actually needed the groove machined in it to work, it also had no hardware. Save yourself a lot of grief and just buy one that is operational. I haven't checked the prices or availability in a while as my whole gun world has turned to AK but I bought one from Pete in New Hampshire a while back for my preban (when that meant something) seems like his website is AR15sales.com I am sure there are many other places like Tapco, etc..
personally I think it belongs on an AR