That is a point I am getting frustrated with most s/o these days. The termination point is very reticent even properly accepting 2 x 2.5 leading to a difficult insertion. Curve, Hamilton, and the cheaper brands all seem to have a crap termination point. I took 3 boxes of sockets back last week and got some MK instead at screwfix. I don't think they are fit for the purpose. Bring back the good old days where you had a half inch round hole (ok slight exaggeration!) to double the cables over in. Try doing that now with the modern sockets. I had a trainee working with me after half an hour he could not terminate the sockets properly. I had to exchange them.