AR Parts Identification

This will be a quick rundown of all assemblies of the AR-15 rifle and each assembly’s components.

Lower Receiver Assembly

Lower Receiver

The only portion actually considered a “firearm”. Everything else is just parts, this requires a background check to be transferred to an individual.

Lower Parts Kit

The lower parts kit fits inside the lower receiver and are a large part of the "guts" of the firearm.

Stock Assembly

The stock assembly is the portion of the AR-15 that allows the AR-15 to recoil and mount to the shoulder of the operator.

Upper Receiver Assembly

Charging Handle Assembly

The charging handle assembly allows the user to cycle the user to cycle the action manually, clear malfunctions and lock the bolt carrier group back.

Forward Assist Assembly

In the event of the rifle being out of battery the forward assist can be used to push the bolt carrier group forward.

Ejection Port Cover Assembly

The ejection port cover assembly is used to keep debris out of the rifle.

Bolt Carrier Group

The bolt carrier group is the component that actually fires the ammunition in the chamber of the rifle.

Upper Receiver

The upper receiver houses the barrel assembly, handguard and bolt carrier group as well as allows the user to use a sighting system on the rifle.

Barrel Nut

The barrel nut is used to retain the barrel to the upper receiver as well as attach the hand guard to the firearm.

Barrel Assembly

The barrel assembly houses the ammunition and the gas block or fixed front sight allowing the excess gas from firing the firearm to be returned to cycle the action.

Front Sight Assembly

The front sight assembly on a standard AR-15 allows the operator/user to fire the firearm accurately as well as pass gas back through the gas tube.

Gas Tube

Gas tube allows the cycling of the firearm and transfers gas from the gas block or fixed front sight to the bolt carrier group.


The handguard of the firearm allows the user to handle the firearm.

Flash Hider

A flash hider is designed to mitigate the flash in night time operations as well as somewhat direct and diffuse the forces coming out of the barrel.

Delta Ring Assembly

The delta ring assembly allows the attachment of plastic handguards.

Lower Parts Kit

Bolt Catch

The bolt catch allows the firearm to hold open on an empty magazine or at the operator’s discretion.

Bolt Catch Plunger

The bolt catch plunger keeps pressure on the bolt catch to keep the bolt catch done under normal firing conditions.

Bolt Catch Roll Pin

The bolt catch roll pin retains the bolt catch and acts as a pivot point for the bolt catch.

Bolt Catch Spring

The bolt catch spring is what pushes the bolt catch plunger against the bolt catch.

Buffer Retainer

The buffer retainer is what keeps the buffer inside the stock assembly when the upper and lower receiver are in the open position.

Buffer Retainer Spring

The buffer retainer spring is what keeps the buffer retainer in the up position.


The disconnector prevents the firearm from firing full auto and allows reliable function of the semi-automatic firearm.

Disconnector Spring

The disconnector spring keeps pressure on the disconnector and the trigger and allows the disconnector to function correctly.


The hammer is what strikes the firing pin causing the chain reaction of events to fire the bullet down range.

Hammer Pin

The hammer pin retains the hammer into the lower receiver and allows it to pivot or rotate.

Hammer Spring

The hammer spring applies the pressure to the hammer and gives it the energy to ignite the primer.

Magazine Catch

The Magazine catch allows the firearm to retain the magazine.

Magazine Catch Button

The magazine catch button allows the firearm to release the magazine.

Magazine Catch Spring

The magazine catch spring ensures that the magazine catch retains the magazine.

Pistol Grip

The pistol grip is where the user’s dominant hand is placed on the firearm and allows operation of the firearm.

Pistol Grip Lock Washer

The pistol grip lock washer prevents the pistol grip screw from coming undone.

Pistol Grip Screw

The pistol grip screw is what keeps the pistol grip attached to the lower receiver.

Pivot Pin

The pivot pin is the front pin on the rifle and is the one that allows the upper to be opened while still being attached to the upper.

Pivot Pin Detent

This prevents the pivot pin from accidentally being removed from the lower receiver.

Pivot Pin Detent Spring

This keeps forward pressure on the pivot pin detent against the pivot pin.


This is what allows the rifle to fire or prevents the firearm from firing depending on which position it is in.

Selector Detent

This keeps the selector in the position you placed it in.

Selector Spring

This keeps pressure on the selector detent.

Takedown Pin Detent

This is what prevents the takedown pin from accidentally being removed from the lower receiver.

Takedown Detent Spring

This keeps pressure on the takedown pin detent.

Takedown Pin

The second of two pins to connect the upper and lower receiver, this one keeps the firearm closed.


This is what the user presses to fire the firearm.

Trigger Guard

In some situations this protects the trigger from being caught on most objects.

Trigger Guard Roll Pin

This pins the trigger guard into place.

Trigger Pin

This aligns the trigger and disconnector while keeping them both in the receiver.

Trigger Spring

Allows the trigger to stay in the ready to fire position before pulling the trigger and returns it to the ready position upon releasing it.

Collapsible Stock assembly

A stock that allows for user adjustment as to length of pull and overall length of the rifle.


This is the piece that interfaces with the user and is separate from the recoil system.

Carbine Receiver Extension

The receiver extension threads into the lower receiver and is the area the stock attaches to.

Castle Nut

The castle nut tightens against the end plate to secure the receiver extension.

End Plate

The end plate helps align the receiver extension and prevents it from rotating in use.


The buffer is a device that helps slow the bolt carrier group down and prevents it from bouncing against the barrel.

Buffer Spring

The buffer spring is the main spring in the recoil assembly.

Fixed Stock Assembly


The fixed stock is a non-adjustable stock that interfaces with the firearm user.

A2 Spacer

The A2 spacer is used to add length to the receiver extension to allow the use of an A2 stock. A1 stocks do not use the spacer.

Receiver Extension

The receiver extension allows the fixed stock.

Rifle Buffer

The rifle buffer is for use with the fixed stock and longer receiver extension.

Charging Handle Assembly

Charging Handle

The charging handle is used to manually cycle the action, which in turn can be used to make the firearm safe as well as load a round into the chamber.

Charging Handle Latch

A charging handle latch locks the charging handle into the upper receiver and unlocks it for cycling the receiver.

Charging Handle Roll Pin

The Charging handle roll pin attaches the latch to the charging handle.

Charging Handle Spring

The charging handle spring keeps the latch in the closed position.

Forward Assist Assembly

Forward Assist

Used for moving the bolt carrier group into battery if it is out of battery or stuck.

Forward Assist Spring

Keeps the forward assist out of the upper receiver when not in use.

Forward Assist Roll Pin

Attaches the forward assist to the upper receiver.

Ejection Port Cover Assembly

Ejection Port Cover

Used to keep debris and foreign materials out of the upper receiver.

Ejection Port Cover Rod

Allows the ejection port cover to be held captive and rotate during operation.

Ejection Port Cover Spring

Keeps the ejection port cover in the open position once it has been opened by the operator or the cycling of the action.

Ejection Port Retainer Clip

Prevents the ejection port cover rod from falling out of the firearm.

Bolt Carrier Group

Bolt Carrier

Houses the components that physically fire the bullet and the piece that actually cycles during operation of the firearm. Loads rounds from the magazine into the barrel.

Gas Key

Allows the action to cycle by transferring gas from the barrel to the bolt carrier group.

Gas Ring

Allows the rifle to build up pressure and send the bolt carrier group rear rearward.

Firing Pin

Strikes the primer on the ammunition to fire the rifle.

Firing Pin Retainer

Completes the assembly of the bolt carrier group.

Bolt Assembly


The extractor is what pulls the brass out of the chamber.

Extractor Spring

The extractor spring keeps pressure on the rear of the extractor allowing it to pivot and capture the rim of the cartridge.

Extractor Pin

Extractor pin keeps the extractor in place and allows the extractor to move when operated.

Vitton O-Ring

The vitton O-ring increases the force the extractor places on the cartridge rim. It is a high temp o-ring so it should not melt under heat.


Ejects the cartridge or spent casing from the upper receiver.

Ejector Spring

Creates the forward pressure to flip the casing.

Ejector Pin

Captures the ejector pin inside of the bolt.

Barrel Assembly

Barrel Extension

Aids with feeding the rounds from the magazine into the chamber. Also indexes the barrel in the upper receiver.


The projectile travels down the barrel to it’s intended destination. Contains the high pressures created by the firing of the projectile.

Fixed Front Sight Assembly

Front Sight Base

Acts as a gas block for directing gas to the bolt carrier group. Also allows the installation of a front sight for creating a sight picture.

Front Sight Post

The front sight post is the forward most portion in the sight picture of an ar-15 style firearm.

Front Sight Detent

Holds the sight in place and allows the sight to be adjusted for elevation.

Front Sight Detent Spring

Creates upward pressure on the detent to prevent the sight post from moving.

Sling Loop

The forward sling loop allows the front sight to be used as an attachment point for a sling.

Sling Loop Rivet

Attaches the sling loop to the front sight base.

Delta Ring Assembly

Delta Ring

Accepts the plastic hand guards in a standard configuration of an AR-15.

Weld Spring

The weld spring creates the forward pressure used to keep captive the plastic handguards.

Barrel Snap Ring

Prevents unintended disassembly of the delta ring assembly.