Kohler k620 tank - which Tank-To-Bowl Connector Kit?
It is always a good idea to replace the tank-to-bowl (TTB) gasket along with the three (or two in some brands) bolts. They can dry up, warp and crack over time and reuse is a bad idea as it probably won't fit exactly. It only takes a pinhole for water to leak. Unless your tank has some indents in the porcelain for the bolts, you can use generic bolts. However, the gasket could be unique to that make and model. Take the old one to the store with you for comparison. You might be able to go with a generic TTB gasket. You can find kits with bolts, washers, nuts and even a gasket, either generic or for your brand. Dome kits now have stainless steel carriage bolts, which ensures they won't rust or rust less. The whole enchilada will set you back only $13.