Made of stainless steel or bronze. Instead of building up a thread hole by welding worn out threads or using bushes for rethreading, you just have to clean the hole with a tap and insert these heli-serts. Tightening procedure is the same as with the original thread. The proper length of the heli-sert should usually be 1 – 2 times the length of the standard bolts being used. Kind of thread: Nominal size, Metric coarse M2.2-M36, Metric Fine M8-M30, Whitworth Coarse W1/4-W1-1/2, Unify Coarse U No.2-U1-1/2, Unify Fine U No.6-U1-1/2, Parallel pipe thread 3/8 3/4