yes the nut is made of nylon and the rod is 10mm in dia if i remember correctly
Why i uses it to hold my rock scape is i can tighten it with nuts from both ends to hold the rocks, that why i prefer threaded rod to fiberglass or PPE rod ... it is efficent if u want to stick 2 short flat rocks to a one pcs long flat rocks. one thing not good about it is can flex if length is too long but when u cut it to length like 3-4in it does not flex...
i uses the expending form to give an additional holding strength to the rocks and rod. Form is chosen over epoxy because it is bouyancy and helps to counter gravity, lighten the rocks and can fill up the gap if the hole is drill too big. Bonding strenght not bad.
Take a look at my new tank thread... u can see the stuff i uses to make my rock scape.
PE rod can be found at a shop next to boon keng MRT selling rubber seals/gaskets ... they close at around 2 to 3 on sat. if u cant find and rubber seals or gaskets to fit you piping you can go there to request them to cut to size for you.
If u need to get any rods look for rods with dia 10mm to 12mm much more easier to find a long drill bits for that size and If drill bits too big your rocks break easily. Get a smaller drill bits which suit your cable ties, it comes in handly if you cant find any holes in your rocks.