This is a Shimano Altus RD-M310 Rear Derailleur.

Features:

Compatible with 7 and 8-Speed shifters
13T upper pulley and 15T lower pulley
Wide link design for more rigidity and precise shifting
Advanced light action
Smartcage pulley plate
Specifications:
Speed: 7 Speed, 8 Speed
Shifter Compatibility: Shimano Road & Mountain
Shift Mechanism: Cable Actuated
Max. Tooth: 34T
Min. Tooth: 11T
Chain Wrap Capacity: 43T
Cage Material: Steel
Chain Retention: –
Color: Black
Weight: 326g