CNC Machined of billet aluminum. Choose the height that you feel comfortable with. Note the 1.5 inch version will be a special production and is for folks that may carrie a lot of weight on the bike or just want to drop it slightly. There seems to be a lot of questions/concerns about which version of the lowering bones is best for you. Here is what we will do. If you get a set and don't like the lowering amount we will swap them for a different height at no charge. All you have to do is send us back the first version you picked. And if you buy them and decide they aren't for you then you can return them to us for a store credit. You are responsible for the shipping back to us and you must do this within 30 days of the original purchase. One thing I won't back down on is that the Lowering Bones are the #1 best thing you can do to make the M109 look cooler without spending a lot of money. In fact, I think its the first thing everyone should do to their M109.