I have used it with standard bars effectively but they are not always a snug fit. It is ok on some movements but not 100% sturdy on others.
The gap is small but I would be hesitant to do any explosive work. On the off chance you were thinking about doing Fat Gripz Snatches with a standard bar I would advise against it! For Curls, Presses etc they should be tolerable.
THIS^^^^ I used then today first time. I noticed when using EZ bar they slid a little bit til they found a spot to stay. Used them on smith machine and worked great!!!