Think the one your thinking of is slightly different but this is what I mean. 
I don't know how affective they are, for me now they're like huh whats this but that might be because I regularly train so its hard for me to say if someone else will find it hard.
If you could get some dumbells, to be honest mate, do you have something heavy that you can grip, is a milk carton heavy to you? Then for now at least perform hammer curls like this:
They are known for training both biceps and forearms, so training forearms will also give you a stronger grip.


I don't know how affective they are, for me now they're like huh whats this but that might be because I regularly train so its hard for me to say if someone else will find it hard.
If you could get some dumbells, to be honest mate, do you have something heavy that you can grip, is a milk carton heavy to you? Then for now at least perform hammer curls like this:

They are known for training both biceps and forearms, so training forearms will also give you a stronger grip.