First of all, high 5 to the seller - my shipment arrived 2 days early on a Sunday, via FedEx - don't often see FedEx's on Sundays!The rails and bearings are well made - the bearings are shipped with retainers to hold the balls in place and sealed in plastic bags, so if a ball did get loose, you will be able to see it - none of mine were loose.The ballscrew and support ends are well-machined and fit accurately together. There is no tightness as one other reviewer suggested. The inclusion of the ball nut housing was a nice touch - other ballscrews I have purchased did not include the housing.My only criticism is the lack of technical drawings with dimensions or a table of dimensions. Happily, the RM1605 seems to be a standard and other manufacturers who supplied these dimensions for their products match this unit exactly.I will buy from them again if I need ballscrews and rails again.My 2 cents