Looks like they may be Dexter axles. The round piece at teh bottom is the brake magnet. Operated by 12 volts through a brake controller on the towing vehicle usually mount on the dash. When actuated causes a magnetic draw to the iron drum and casues the mechanism to move applying the brake pads to the drum. You should be able to get parts at places like NAPA and trailer shops. If you need a magnet and shoes sometime is is alot simpler to get new backing plates and it come complete for not much more money and a whole lot of saved time. GOod luck.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7