Omega rails connect the upper and lower components together with four screws on the 7 and 9 inch and 6 screws on the 12 inch making for an extremely secure fit and the precision of the CNC machine on these Aluminium components means the tolerance is so tight that they slide together and hold almost with a friction fit as is.
Madbull offers Omega X rail systems in 7, 9 and 12 inch versions, so take a good think about which ones suits your weapon better.
7 Inch rails are rather short, a standard M4A1 rail system will be around 9 inches. 7 inch RIS front sets are good for SBRs (Short Barreled Rifles) as it will comfortably take 7 to 12 inch outer barrels without looking too absurd.
9 Inch rails are about perfect for the M4 length of carbine length barrels. Putting a shorter CQB barrel in it is still good but you can push that right up to M4A1 14.5 or even a a little beyond and still look good
12 inch rails are rather long, they can take 14.5 M4A1 length barrels rather more snugly then a normal rail and can go right up to an M16 20 inch barrel and still look the part. That said, the 12 inch Omega rail is designed with a gap in the upper for the M4A1 positioned front sight, with the rest of the length covering the remaining outer barrel length.
These rails come with both upper and lower components, a barrel nut and screws for attachment. These rails will fit standard M16 family Marui/G&P compatible type weapons.