I've got a couple Loki rifles with the 15" carbon fiber handguard on it. Great piece that's sturdy and easy to mount. Much easier than the Clark carbon fiber piece from the past. Like was stated above, barrel nut with a ring in front of it that the tube attaches to with 3 torx head screws and then a lock ring on the front of the barrel nut. Easy to install, remove, etc. I had gas issues on the range with my JP low pro gas block and the handguard was easily removed for adjusting (could have adjusted it with a ball tip allen wrench if I had one).
Loki makes great products. I love their 16" nitride barrels. The 18" double fluted barrel I have shot a 2.25" group at 300 yards. Their billet upper/lower sets are really nice too.