Before ordering this set of truss rod wrenches, check your gear to make sure these tools are made to work with the truss rods on your instruments. I have 20 stringed instruments with differing requirements for types and sizes of truss rod adjustment tools. If you have instruments with male hex ends in the sizes of 1/4" (6.35mm), 7.0 mm, or 5/16" (8.0 mm), this kit will work for you. If you have truss rods with female hex adjustment ends, consider instead the Musiclily Pro Hardened Steel 5Pcs Allen Keys Hex Wrenches Set for Guitar Bass Truss Rod Adjustment. If you have several guitars with both types of truss rod adjustment ends, then the purchase of both kits will serve your needs well. This is a pro quality all-metal set. The handles are thick, with a diamond stamped pattern that makes them easy to grip. Who needs truss rod adjustment tools? 1) If the string action on your guitar or bass is too high or too low. 2) If you need to change string gauge to thicker or thinner strings. I used the 5/16" tool in this kit to lower the string action (by loosening the neck truss rod tension) on my Peavey Generation guitar. The tool worked well with a correct angle and fit to make the adjustment. I like to set my string action as low as it will go without getting fret buzz with a medium pick attack. If you change string gauge or make truss adjustments, you will also want to check the intonation on each string and adjust if needed. Of course, there are a lot of other things to consider such as saddle height, floating bridge spring tension and height, nut size and height, and fret height, but truss rod adjustments and intonation are a good place to start. This is a good professional-quality kit.