In an industrial accident at the age of 17 on his last day of work in a sheet metal factory, he lost the tips of the middle and ring finger of his right hand. Iommi considered abandoning music, but his boss (who knew of Iommi's "night job" as a pub band guitar player) encouraged him to reconsider by playing a record by jazz guitarist Django Reinhardt, who earned wide acclaim despite limited use of his fretting hand following an injury.
After attempting to learn to play right-handed , Iommi strung his guitars with extra-light strings (using banjo strings , which were a lighter gauge than even the lightest guitar-strings of the time) and wore plastic covers over the two damaged fingers. He fashioned the latter himself, by melting plastic liquid-soap bottles into a ball and then using a soldering iron to make holes into this ball, putting his fingers in while the plastic was still soft enough to be shaped. He then trimmed and sanded away the excess plastic to leave himself with two thimbles, which he then covered with leather, to provide better grip on the strings. Subsequent tips have been custom-made.
is aforementioned factory accident impacted the Black Sabbath sound later on, as Iommi detuned his guitar from E to C# (3 half-steps down), in order to ease the tension on his fingers. As a result, Sabbath were among the first bands to detune and resulted in the technique being a mainstay of heavy metal music