Unfortunately, all bases, rings, and actions are not manufactured in perfect alignment with each other. Whether you have a one-piece or two-piece base, the odds are against you that your rings will be in perfect alignment. Why chance putting your scope in a bind, whether it is a $200 scope or a $1000+ scope? The Sinclair Scope Ring Lapping Tools are designed to correct the misalignment of scope rings. The Sinclair Scope Ring Lapping Tool is used to align the rings first and then to remove just enough metal from the scope ring bearing surface to fine tune the alignment. Misaligned rings actually cause your scope's main tube to bend, causing distortion and requiring you to use excessive amounts of windage and elevation which moves the scope farther from its optical center. The farther you are from the optical center, the more likely you are to have distortion and a darker sight picture. Sinclair Scope Ring Lapping Tools ( 1 inch, 30mm, 34mm, 35mm) are made from ground accuracy stock stainless steel that has a tolerance of +/-.0005 inch. Each Sinclair Lapping Tool comes with the lapping bars are 10 inch in length, which gives you plenty of stroke length to quickly lap your scope rings.