The pilot/owner of the amateur-built airplane reported that, while performing touch-and-go landings, he failed to properly flare the airplane resulting in a hard landing. The landing loads exceeded the strength of the main landing gear attachment, which resulted in a separation of the main landing gear. The airplane subsequently departed the left side of the runway and struck the visual approach slope indicator lights, resulting in substantial damage to the right wing strut. The pilot/owner’s postaccident examination revealed that the aftermarket landing gear installation had been improperly installed. The attachment bolts had been overtorqued which preloaded and overstressed the hardware, reducing the load-carrying capability. The stripped attachment bolts allowed the clamping brackets to separate under load. The hard landing exceeded the reduced capacity of the landing gear attachment, resulting in a separation of the landing gear and a subsequent runway excursion.