How to confirm the length of extended bolts?
Generally, it’s easy to figure out the correct size of bolt, all you need to do is to measure the length of your stock bolt then add the thickness of the required spacer, and that will be your ideal extended bolt length. In most cases, you need a bolt that is longer by the thickness of the spacer, for example, your stock bolts are 27mm, the desired spacer is 12mm, then the right size of extended bolts would be 39mm. But there can be exceptions. Considering the critical importance of the length of thread fully engaged in the axle hub, it’s always best to measure from the wheel bolt you’re currently using.