Product details:

Outside Diameter, 647 lbs./in. Rate, 1.070 in. They're manufactured from super-clean, high-tensile chrome silicon steel and are shot-peened to MIL specs for maximum fatigue life. They feature a proprietary, multi-step heat-treating that minimizes load loss and have computer-aided modeling to minimize valve bounce and valve gear separation. The Manley NexTek valve springs are smaller diameter and lightweight, allowing engines to rev higher faster. They have an extended tip thickness designed to eliminate overload breakage, and their tightly controlled open-end flatness reduces valve stem side loading.