I bought the first set of collets, received them and found the "collet nut" was not machined properly. This prevents the chamfer on the collet from engaging the collet nut so that it can be tightened. So I sent it back and received the same product today and guess what, it has the exact same problem. I am now returning a second item for a refund and will be looking for a different brand of ER40 collet set. The Accusize salesman was very helpful and responded quickly but was unable to easily send me a working "lock nut". The overall quality of the parts in the kit looked great with the exception of the jam nut. Their entire inventory must be pulled out and inspected for this defect or they will incur huge shipping bills.