Ok, so I was looking at these on Ranglebox.com: http://ranglebox.com/mechanical-products/

Just wondering if this is needed to join HDPE together, or can HDPE sheets be bolted directly to each other, without any joining elements? If it is necessary, would it be the M4 or M6 threaded bar I'd need?
And also, how would one go about cutting the bar to size? Is an angle grinder necessary?
I know this was mentioned on this thread by Flag Captured a while ago now - sorry for not asking about it sooner!

I'm a little bit away actually building much at the moment as I'm still having problems with the drill chucks from hell. None of my local shops had torx screwdrivers, but I'm going to a hobby shop in another town tomorrow so hopefully I can get this sorted!