The 7100 Housing Comparison Gauge (Left-Opening) is an essential tool for auto parts suppliers and starter rebuilders. It is designed to compare old left straight mount starters with new replacement starters, allowing you to identify the number of shims needed to correct flywheel engagement. This gauge is specifically used on Delco starters, ensuring compatibility. it provides accurate measurements and saves time when selecting the correct shims for a starter install. When you're working on older vehicles models, this gauge will help you ensure a perfect fit and optimal performance.