These light-weight brackets (under 15 g each) are specifically designed for the Pololu 37D mm metal gearmotors, such as the 19:1 metal gearmotor 37Dx52L mm. Each bracket features seven mounting holes for M3 or #4-size screws along each edge, giving you a variety of mounting options. A total of twelve M3 screws (six for each bracket) are included for securing the motor to the bracket.
The hub pictured works nicely with this bracket.
