spark plug needed for McCulloch MD320AV ?

i have the above strimmer and need a new spark plug for it as i bought it from someone very cheap as it did not have one. i can find the schematics for it on the net but they don't come with model numbers for the parts needed for the strimmer. so im asking the knowledge of earth for this simple answer that im not blessed with knowing.

thankyou for reading

yours sincerely

silkykameron