I carried a Safe Keeper I (now out of production) for a couple years in sketchy areas. The Safe Keepers have normally ground dagger shaped blades. The Safe Makers appear to be ground normally on one side, and the back is ground on a LARGE diameter wheel. When you lay that side flat on the table, only the edges will make contact. The center will be off the table a bit, depending on how big the wheel was. I've heard of wheels for this type of grinding being as large as 4 feet in diameter. Sushi knives also use this type of grind on the back sometimes.