1/2-28 for ya on the end Grant Stace makes a nice adapter for Silencers but he only does 1/2-20 maybe he could help ya out with something ya never know about Ol Grant ???? Must be nice not to have to go through all the Red tape & paperwork in the UK

Here it is pretty easy to get them but the paperwork & Red tape can be a pain....
Just when I thought I had all my bases cover in the Hobby department I came across this most excellent Airgun forum, Now the madness begins....."PROTOSNIPER"