Here's my new CAR-15 Fiberlite reproduction synthetic buttstock from Brownells (trying it on my son's Colt LE6920 M4 carbine), it looks exactly like the Colt Fiberlite stock that I had on my Colt AR-15A2 Sporter II carbine way back in 1985 when I bought it new.
These stocks are mil-spec size for mil-spec size receiver extensions (buffer tubes) and made by a reputable US company B5 Systems which makes the Enhanced SOPMOD stocks for the US military.
There is a hidden symbol letter stylized "B" same as the font of B5 Systems on SOPMOD stocks, behind the adjustment lever.
The hard to find original Colt CAR-15 Fiberlite sometimes called N1 (with N1 Markings - some have no markings) are very expensive now new to excellent condition sliding buttstock only are from $200+ up to $300 currently.
I'm glad they had these now, before you never know the quality of the different makes. These have very little movements and looks exactly like the factory original.
This type of stock are ideal for the XM177 clone builders, mid '80s to early 2000s models or early M4 carbine retro builds.
This stocks was replaced by the current M4 waffle type stocks type 2 gen 4 with 4 position receiver extensions in 2002.
For guys interested in these stocks they're on sale now at a lower price, regular cost was $42.99 (I'm not sponsored by Brownells, just a long time customer).