assurance tested, more responsive, less expensive, easier to install. Improve the accuracy of measuring bottlenecks, extends brass life. More accurate measurement of changes in the firing or size adjustment of brass to improve safety. The small screws on the comparator body can be adjusted to fix the bushing. How to determine the proper bushing diameter: Add the neck diameter and shoulder diameter and divide that number by 2, use the bushing that is closest to that number. Application: For A330, C375, D400, B350 and E420. Compatible with Checking Most Bottlenecks. Vehicle compatibility charts are for REFERENCE ONLY. Checkproduct type and sizeto match your needs. Note: Installation guide not included, we strongly recommend you professional installation. Please check as much as possible to make sure the item is what you need. Colour: Material:plastic Package Contents: 1x Gauge Body 5x Bushing