It used an electromagnet that he had designed to magnetize the spikes;
(It; used; an electromagnet that he had designed to magnetize the spikes) (an electromagnet; had designed; to magnetize the spikes) Context(an electromagnet had designed,List([8, 45))):(he; to magnetize; the spikes)
an electromagnet had designed,List([8, 45))
It an electromagnet he
used had designed to magnetize
an electromagnet that he had designed to magnetize the spikes
to magnetize the spikes
the spikes