<https://china-timing-pulley.com/whats-the-difference-between-spur-helical-bevel-and-worm-gears/#primaryimage>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://china-timing-pulley.com/whats-the-difference-between-spur-helical-bevel-and-worm-gears/>