Park's Lockring Wrench is for installing and removing the adjustable-cup lockring used on Dura-Ace and XTR bottom brackets that use a left-side lockring (it fits several other models and brands of lockrings, too). The Lockring Wrench is laser cut and engages 5 of the lockring's 6 notches for a precise, secure fit. The vinyl-coated handle offers a great grip, too.
The major diameter of this tool is nominally 46.5mm. The minor diameter (at the notches), is nominally 41mm.