These are being made for us by Warwick Machine Shop in Landisville, PA. We have seen and used many different upper receiver action blocks but all of them seem to come up short of what we needed. So we hooked up with Warwick and worked with them on a design that fills those voids. First the lower block is reversible so it does not matter which end is forward or back... It also features stainless steel pins for durability. Next, the top block has four tension allen head screws to allow for as tight of a fit as the user needs or wants. We also designed the top part of the block to be able to slide out past the upper so it can be used to help align forearm rails as well! This is a top quality action block set that will serve you well for years to come and is a must have tool for the avid AR15 enthusiast! Price includes Free USPS Priority mail shipping! (if purchased with other items that do not include free shipping the website will not include the weight of this item in the shipping cost calculation)