Spacers are you may know makes your vehicle wider. It makes your wheels stick out and helps makes the handling better. I went with H&R Spacers and they are made in germany. I must say, they are awesome products and if available, they have something specifically made for your vehicle. The X5 compared to X5m has 74.01 wheel hub bore boht front and rear (X5m has 72.xx in the rear) so having these spacers in my X5 makes the ride smoother and agressive. These are 25mm in the rear and 20mm in the front spacers. The H&R brand I purchased came with the longer bolts 14x1.25x50mm in the rear and 14x1.25x45 in ther front. As you can see on the picture below, the rear spacers are bolt-in, so the spacer gets bolted onto the hub and wheels onto the spacer. I questioned the safety but they engineered it and no reports of failure and I am sure I wasn't the first to ask the question.