Cob size gear is designed to fit horses that are between the size of a pony and a full-sized horse, typically those with a height of 14.2 to 15.2 hands. Pony size gear, on the other hand, is specifically made for smaller horses, usually under 14.2 hands. Cob size gear accommodates horses with a shorter, stockier frame, while pony size gear is tailored for the smaller dimensions and build of ponies.