The body is plastic, but it has a metal thread, size 1/2" 20 tpi (UNF).
This sale is for Adapter only, which is a replacement of the original front sight.
Fitting instructions:
Knock out the pivoting pin at the front. Try both directions to find which way it goes out easier. Remove the original front sight ant replace it with the new one. Before you hummer the pin back in make sure the holes in the tube and the adapter are properly aligned, otherwise you will break the adapter.
With the new adapter you do not really need the plastic spacer between the barrel and the tube, but if you wish to fit it back, you can just shorten it a bit. Align the holes and put back the pin to secure the adapter in place.
Contact me for advice on silencers.