Level Frets with Full String Tension Achieve professional fret leveling without removing the strings! The StewMac Fretbar Understring Leveler is a revolutionary tool that allows you to level frets under full tension, ensuring precise and accurate results. Designed to fit under and between the strings, this tool eliminates guesswork and helps you achieve perfect fretwork every time.The Original Understring Leveler – by StewMac This innovative tool was developed based on a brilliant idea from Matt Brewster of 30th Street Guitars, who brought us the concept of fret leveling with the strings still on. StewMac transformed this idea into the Fretbar Understring Leveler, making professional fretwork faster, easier, and more accurate.Precision Engineering for Luthiers & Guitar Techs Crafted from durable extruded 6061 aluminum, the Fretbar guarantees a surface accuracy of ±0.0015" per foot. It works seamlessly with our 1" wide 3M Stikit Gold Abrasives, allowing for quick setup and ultra-smooth leveling.Versatile Sizes for Every Fret Job Choose the perfect Fretbar length for your needs:4.5" Fretbar: Ideal for spot-leveling and creating fallaway on acoustic guitars.9" Fretbar: Great for ukuleles, mandolins, and full-scale spot leveling.18" Fretbar: Quickly levels an entire neck with precision and ease.Includes the StewMac String Jack The included String Jack lets you raise the strings at the nut without altering neck tension, ensuring accurate leveling results.Works with Strings On or Off While designed for under-string leveling, the Fretbar is also a highly effective all-around fret leveling tool when used with the strings removed.BUILT TO LAST A LIFETIME, WITH SUPPORT YOU CAN TRUST StewMac’s Lifetime Promise ensures our tools are made to last. But we don’t just stand behind our products—we stand behind you. Our team of expert techs is always available to offer guidance and support.