Please read note how to install before you do - NcSTAR AR-15 Picatinny Handguard Rail

These fit absolutely perfect on carbine or full length hand guards. That being said you need to remove your heat shields and put the inserts in underneath of the heat shields or the screws will not be long enough this is intentional. You may have to open up the holes by a fraction as you do not want to open them up all the way you want to press them in for them to fit snugly underneath the handguards. This is all you need to do to make them fit right you do not need to go buy extra screws or nuts. This is why you can put them on the top or bottom handguard.