Zenport Finger Knife RK12-10PK Finger Knife, Size 12, Finger Knives, BAG OF 10

Zenport Finger Knife RK12-10PK Ring Knife, Size 12, Finger Knives, Finger knives can be worn on the finger for cutting tape, opening boxes. Used for cutting. Also an excellent and inexpensive harvesting tool. 

Available in a variety of sizes. 

(Note: some put these on their pointer finger or over a glove which would require a larger ring size than your ring finger)