LSM Racing Products' On-Head Valve Spring Testers are designed for various shaft and stud mount style roller rocker systems, great for big blocks, small blocks and big chief style. They feature four course adjustment hole locations and include four fine adjustment shims which enable calibration to within .050" of rocker arm pivot length. They come equipped with a 0-600 lb. liquid filled gauge, improved billet steel rocker hook and includes set-up and adjustment guide.