ptfe tape
ptfe is what i use,lts of it around the thread should do the job
No chaps you misunderstand, i can get it on tight its just a nightmare trying to get it on straight and the right way up. I can do it, BUT I JUST WONDERED IF THERE WAS A WAY TO DO IT I.E. bristles facing down when you start to tighten etc I never get it right first time there seems to be no technique to learn either.