This is a muffler earth product, known for improving fuel efficiency and increasing torque. With gasoline prices remaining high, it's recommended for those who want to improve fuel economy, whether for driving, leisure trips, visiting family, daily commutes, or shopping! Sold as a set of 4. Total Length: Approximately 30 cm (Please allow for a few millimeters of error) Terminal Size: 8mm (Suitable for M8 bolts) We also have 25 cm lengths in stock, so we can accommodate changes to a combination of 30 cm and 25 cm. If you would like to change the lengths, please leave a comment. Muffler earth is popular as an easy tuning option because it's easy to install and can be expected to improve fuel efficiency and torque. You can also install it on the muffler side using metal bands for hoses, etc., so it doesn't matter what type of car you have. (Bands are not included, so you will need to prepare bands separately if you use them for installation) ⚠ Although it can be installed on various car models, please research the compatibility, the required cable length, and the actual installation yourself. Instructions are not included. ⚠ To get the most out of the muffler earth's effects, please remove rust, dirt, and paint from the installation area and ensure that the metal part and the terminal are in contact during installation.