About Helicoil Twinserts: Twinserts are two Helicoil wire inserts, one fitted inside the other. An Outer Helicoil insert is installed into an oversized tapped hole (which is larger than that of a usual wire thread insert tapped hole) which then, an Inner Helicoil insert is fitted inside to give a standard female thread. The Outer insert is installed into the Twin sert tapped hole and has the same nominal length as the original thread. The outer insert is always free running while the inner insert can be free running or screw locking. Twin serts are used for the repair and recovery of tapped holes that are stripped, have widespread cracks, or are off-centre.