**Solution:**

Given diameter of copper rod, d = 1 cm

Hence its radius, R= (1/2) cm

Height of rod, H = length of rod = 8 cm

∴ Volume of rod = πR^{2}H cubic units

= π x (1/2)^{2} x 8 cubic cm

= 2π cubic cm

Given that cylindrical rod is drawn into a cylindrical wire of length, h = 18 m

That is, h = 1800 cm

∴ Volume of cylindrical rod = Volume of cylindrical wire

Let r be the radius of the wire

Hence 2π = πr^{2}h

That is, 2 = r^{2} x 1800

r^{2} = (1/900)

Therefore, r = (1/30) cm = 1/3 mm

Diameter or thickness = 2(1/3) = (2/3) mm