The Corbeau BMW E21 seat brackets are manufactured to be a direct bolt in to the BMW E21 chassis. Direct bolt in means your bracket will bolt to the existing bolt holes in your floor board with little to no modifications. Corbeau BMW seat brackets are powder coated in a black wrinkle finish and come standard with single locking sliders. Single locking sliders have a handle on the locking side that you pull to the side to slide your seat forward and back. You can upgrade to a double locking slider for an additional fee. Double locking sliders have a bar that connects the two locking sliders and you pull up on this bar to slide your seat forward and back. If you do high stress driving of any kind we recommend a double locking slider.