Most high performance engines require larger than stock diameter valve springs. Our Spring Seat Cutters allow you to machine the spring seats using an ordinary hand drill. We even offer seat cutters to accommodate the spring seat cups that are so widely used today (Note: all seat cutters cut to .630" inside diameter). Our Valve Guide Cutters are designed to shorten the valve guide boss for high lift cams, and also reduce the outside diameter to accept triple springs and/or aftermarket valve seals. Each tool utilizes our Interchangeable Arbors, which are sold separately, so order the one that matches your valve stem diameter.