a helicoil is NOT a next size bolt, It's a stainless steel thread insert that is screwed into the hole. The end result is a thread that is stronger than the original one was when it was new and the standard stud remains in use. It requires a special kit with the inserts a tapping drill and tap, and a tool th wind the inset into the freshly tapped hole.
Helicoil is just one brand name, tends to be the one everyone uses just like we all call vacuum cleaners 'hoovers'
I use a 'Re-Coil' kit...just another brand