Cianbro worker Kyle Chapman guides the south “bull gear” Thursday as a crane lowers it into position on the Mystic River Bridge.

The approximately 10,000-pound gear is the last major piece of the two-and-a-half-year, $15 million restoration of the 90-year-old bascule drawbridge linking Groton and Stonington.

The smaller pinion gears and the electric motors that will raise and lower the bridge are expected to be installed in the next week. The project is scheduled to be complete by April 15.