Unexpected profit lifts Altra the most ever

Braintree-based Altra Holdings Inc.’s stock rose 18 percent, the most since its initial public offering in December 2006. The shares were upgraded to “outperform’’ from “neutral’’ by Robert W. Baird Ltd. after Altra posted an unexpected profit in the third quarter. Altra’s website says it is a leading producer of a wide range of mechanical power transmission products frequently used in critical applications, such as fail-safe brakes for elevators, wheelchairs, and forklifts. It also provides products for high-volume manufacturing processes.