As far as the material goes, there are rods, robots, race-cars, rakes (?), and rings.
If you consider 'Metal' the genre of music, then you could use Rob Zombie.
The Red Square begins with R.
Rum is a liquid. It begins with the letter r.
Put Romano cheese on a pizza. It begins with R.
Round is the opposite of square. It begins with the letter r.
Robbery is a sad word. It begins with the letter R.
there is a metal knuckles but only in one game and its sonic r and the closest thing to a metal tails is the tails doll
a 4 letter word that begins with r is rice
Put Romano cheese on a pizza. It begins with R.
Radiant describes a star. It begins with R.
A synonym for mother that begins with R is relative.
Robotic surgery is a technology. It begins with the letter r.
Robotic surgery is a modern technology. It begins with the letter R.