TACPOOL AR-15 Glossary

1 – Handguard; 2 – Gas Tube Roll Pin; 3 – Gas Tube; 4 – Flash Suppressor; 5 – Peel Washer; 6 – Handguard Retaining Ring; 7 – Spring Weld Assembly; 8 – Delta Ring; 9 – Upper Receiver; 10 – Barrel.


A2 Style Front Sight – Combination gas block and front sight, common on AR15 rifles.

AR-10 Rifle – A .308 rifle made by ArmaLite, ArmaLite owns the trademark of the AR-10 name

AR-10 Style Rifle – Semi Automatic .308 rifles made by various manufacturers resembling an AR-10 design. Many parts between manufacturers are generally not interchangeable.   

AR-15 Rifle – A lightweight, air-cooled, magazine-fed rotating bolt rifle. Originally designed in 1957 by Eugene Stoner, it is the most popular rifle in the United States

Barrel Nut – A nut that screws onto the front of the upper receiver, designed to attach and hold a free floating handguard

Bolt Carrier Group (BCG) – A component of the upper receiver, it controls the feeding, firing and ejection of ammunition.

Carbine gas system – Gas port distance of 7”, barrel length generally 10-18” (Most AR15 rifles use this system)

Delta Ring Assembly – Used to retain handguards in place by applying pressure from the weld spring. Not used if installing a Free Floating Handguards. Contains the handguard snap ring, weld spring and handguard slip ring.

Direct Impingement Gas System – Original AR design and the most commonly used on AR15 rifles. Uses gas generated by the firing on ammunition to cycle the bolt

Drop in Quad Rail Handguard – Easy and quick to install, held together in place by the delta ring and front sight post/gas block

Free Floating Quad Rail Handguard – Harder to install, held in place only by the barrel nut attached to the upper receiver. They do not touch the barrel at any point allowing for free barrel movement during firing resulting in greater accuracy

Front Sight Taper Pin – Used to hold the front sight/gas block in place on the barrel

Gas block – The gas block fits over the barrel, allowing the escaping gasses to go back to the upper receiver to cycle the bolt

Gas Piston System – Uses gas generated by the firing of ammunition to push a piston which cycles the bolt (Used by the AK family of rifles). Please note – Monstrum Tactical does not carry rails compatible with piston system AR-15 rifles.

Gas Tube – Tube connecting the gas block to the upper receiver

Gas Tube Roll Pin – Secures the gas tube onto the rifle

Handguard – Installed over the barrel to protect your hands from the heat generated by operating the weapon, also provides a place to grip the weapon

Keymod Handguard – Free floating handguards that allow the user to attach picatinny rails in various places allowing for greater customization

Low profile gas block – A gas block designed to be small and compact so that it will fit inside a free floating quad rail, allowing for its installation and use

LR-308 – A .308 rifle made by DPMS, this style of receiver has been widely adopted by various manufacturers. Monstrum Tactical LR-308 rails are compatible with this style of rifles

M-LOK – A rail system developed by Magpul that allows for the attachment of compatible accessories. 

Mid Length gas system – Gas port distance of 9”, barrel length generally 14-20”

Muzzle break/Flash Hider/Compensator – Attaches to the end of the barrel, designed to reduce muzzle flash, muzzle rise and recoil

Picatinny rail – A standardized bracket allowing for the attachment of various compatible accessories

Pistol gas system – Gas port distance of 4”, barrel length is generally 10” or less

Quad Rail Handguards – Handguards with rails (usually picatinny style), these allow for the attachment of various accessories such as grips, lights, optics, etc. Generally available in two styles

Rifle Length gas system – Gas port distance of 12”, barrel length generally 16” or more

Upper receiver – Holds the bolt, barrel and handguard. Attaches to the lower receiver completing the firearm

Weaver rail – A predecessor to the Picatinny rail. Generally, accessories designed for Picatinny rails will fit on a Weaver rail, but not vice versa