@MamoruHisaishi , I do not know where you live in the world. There is a nasty new trend in English being spoken in Britain, where many people are using the singular 'is' instead of the correct 'are'. I don't know whether this trend has come from somewhere else but I suspect it has and I have a good idea where from. It is widely prevalent. I have definitely heard a Member of Parliament make the mistake and I think I heard the well-educated Prime Minister do it. If I catch him do it, and I am quite sure he has done, I will drop him a line, because there's no point in educating children if they are not taught correctly, and they should hear good examples.
I do not know whether you 'picked up' your English or whether you had formal lessons. If you had formal lessons you will have met: I am, you are, he/she/it is, we are, you are, they are. Stick with the correct 'the threads are about him' and resist any insidious trendy-wendies who would influence you to say 'the threads is'.
I expect I will have to be hung in a cage outside the town hall, having written this post.