It wasn't an OEM part. I had seen an instagram post from Briley announcing a "coming soon" 6 position buffer tube. So when I sent in my M4, I had requested the 6 position tube be added to the order. I think that is why it took so long to get it back. When I had called to check on the status, they told me that the tube had not gone into retail production yet, so I assume it's Briley's in house tube, but they were going to get one for me. The invoice shows they charged me $249.95 for the tube and no charge for the gunsmithing labor to install it due to the wait time. I've seen the posts from RXarms and his tube sounds awesome with a great price, especially with the position markings, which mine does not have. However, I feel I got a decent deal due to not having to pay the labor to install the buffer tube. I like the 6 positions mainly because it lets me dial in the length a little better to make the perfect cheek weld for the optic.