you can buy some plain rail, drill and tap your holes where you want them in the FF, just like you would do for a sling swivel stud. then bolt the rail to whatever side you are using. i always tap the holes and then put a locknut on it as well since foregrips can stress the connection. also use long enough of a rail so that you can put 3 bolts through it, each end and the middle. pretty easy, take your time. if you don't want to take the tube off you can do it with it on, just be careful with the drill. get a long set of hemostats to use to put the nut on the bolt, tighten from bolt head side.
