AR 15 Parts Diagram | AR 15 Parts List

The Complete AR 15 Parts Diagram with AR 15 Parts List and all AR 15 Parts Labeled 


AR 15 Parts Diagram | AR 15 Parts List

The AR 15 Parts Diagram is an essential visual guide that breaks down the intricate components of this popular rifle platform. It provides a comprehensive understanding of how each part interacts with others to form a functional and reliable firearm. From the upper and lower receivers to the bolt carrier group, gas system, and trigger assembly, the diagram highlights the key elements that make up the AR-15's design. Whether you're a firearm enthusiast, a gunsmith, or a first-time owner, this diagram serves as an invaluable reference, aiding in maintenance, customization, and troubleshooting to ensure optimal performance of your AR-15. For more in-depth information on how to build an AR-15, please check out our other comprehensive guide available on our blog.

1. Firing Pin

The firing pin is the part of the weapon that is used to strike and activate the primer in the round. There are different firing pins including Mil-Spec and Extended Firing Pin.

2. Bolt Carrier

The bolt carrier body makes up the bulk of the bolt carrier. It comes in various finishes and shapes. The most popular is the Black Nitride BCG.

3. Firing Pin Retaining Pin

This is typically made from hardened steel and holds the firing pin in its spot inside the bolt carrier. It keeps the firing pin from coming completely out, but allows it to freely move back and forth when struck by the hammer.

4. Bolt Carrier Key Screws

There are two bolt carrier key screws. Be sure to check and see that the key screws are properly staked in order to keep them from retracting during use.

5. Bolt Carrier Key

The bolt carrier key is the part o the BCG that fits in place over the gas tube. When a round is fired and the captured gas is sent through the gas tube to the BCG, it is used by the bolt carrier key to send the BCG backwards; removing the spent round and chambering a live round from the top of the inserted magazine.

6. Cam Pin

The bolt cam pin rotates the bolt so it locks up in the barrel extension. This ensures there is a tight fit when the next round is fired, keeping the action of the rifle reliable and safe.

7. Bolt Gas Rings

This set of three elastic gas rings seal the gap between the internal cylinder walls of the carrier and the bolt. It functions much the same way a piston in an internal combustion engine works.

8. Bolt

The bolt blocks the rear part of the gun chamber, at the rear of the barrel, while the propellant is actively burning, forcing the expanding gases to push the projectile forward. Once the projectile has been fired, the bolt moves back removing the spent round and presses a new cartridge into the chamber on its way forward.

9. Extractor Spring

This small spring is what maintains the tension on the extractor. The part of the BCG that grips the spent round as it is pulled from the barrel.

10. Extractor Spring Insert

This is a small black neoprene insert shaped like a top-hat. It rests within the Extractor Spring and helps stabilize the spring and act as a shock absorber for the Extractor.

11. Extractor

This is the part of the BCG that removes the spent casings of the fired cartridges from the chamber. his allows for immediate loading a fresh round of ammunition.

12. Extractor Pin

This pin keeps the extractor in place and provides a pivot point to allow for release of the spent round.

13. Ejector Roll Pin

This pin holds the ejector in place inside the bolt. It is a retaining pin that keeps the ejector in the hole, in the bolt, while the ejector spring provides tension to eject the spent round after extraction has taken place.

14. Ejector Spring

This important little spring is what provides the force to eject the round after the extractor pulls the spent round from the barrel.

15. Ejector

The little but mighty part that forces the spent round out of the extractor with the force from the ejector spring.

16. Charging Handle Latch Roll Pin

This little roll pin holds the latch to the handle. It also provides a pivot point for the latch to actuate.

17. Charging Handle Latch

This is the latch that is used to disengage the handle from the receiver and allow it to be pulled back.

18. Charging Handle Latch Spring

This spring is what maintains the tension on the latch to keep the handle securely in place during standard operation.

19. Charging Handle

This is the handle body that makes up the bulk of the charging handle assembly.

20. Rear Sight Helical Spring

This small spring acts as the mechanism for maintaining tension on the sight bearing in the windage adjustment knob.

21. Rear Sight Windage Knob

This is the adjustment knob in the rear sight to allow for windage adjustments for fine tuning aiming.

22. Rear Sight Windage Knob Pin

This pin holds the knob secure to the windage screw, so the aperture moves left or right when the knob is spun in either direction.

23. Rear Sight Ball Bearing

This ball bearing is used to maintain tension on the windage knob so it holds in place after being set.

24. Rear Sight Base

This is the base or body of the rear sight.

25. Rear Sight Windage Screw

This is the screw that pins to the windage knob allowing the knob to be turned and fine tune the aperture of the sight.

26. Rear Sight Helical Spring

This spring maintains tension on the ball bearing in the sight.

27. Rear Sight Ball Bearing

This ball bearing is used to maintain tension in the sight.

28. Rear Sight Aperture

This is the part of the sight that is looked directly through to zero in where the desired location of the fired projectile will end up.

29. Rear Sight Flat Spring

This spring holds tension on the aperture keeping it in place. It also allows for the aperture to be flipped forward or back swapping between aperture hole sizes.

30. Index Screw

This indexing screw ensures the sight is facing directly forward.

31. Black Rifle Depot Logo

This highly trusted logo ensures that you are always getting top quality AR products at extremely fair prices with great service and fast shipping.

32. Index, Elevation

This is the part of the sight post that allows for elevation changes or fine tuning of the sight.

33. Knob, Elevation

This is the knob used to adjust the elevation of the sight.

34. Ball Bearing

This little bearing is used to apply tension to the elevation post of the rear sight.

35. Index Spring

This spring is used to apply tension to the ball bearing in the elevation index portion of the rear sight.

36. Elevation Spring

A larger spring used to hold the elevation portion of the rear sight in place.

37. Forged Carry Handle

This is the forged body of the carry handle rear sight assembly.

38. Rear Sight Elevation Spring Pin

This pin holds the elevation spring in place.

39. Cross Bolt (2)

These two bolts are responsible for holding and locking the carry handle rear sight assembly to the picatinny rail on the top of the upper receiver.

40. Thumb Nut Assembly

These two thumb nuts make it easy to tighten the cross bolts. It makes installation and removal of the rear sight/handle assembly a tool free process.

41. Clamping bar

This is the tension bar held in place by the thumb nuts and cross bolts that keeps the rear sight/handle in place.

42. Forward Assist Spring Pin

This pin keeps the forward assist plunger in place.

43. Forward Assist Plunger

The part of the forward assist that would be pressed, or forced forward in a necessary situation.

44. Pawl Spring Pin

This pin is part of the pawl assembly in the forward assist. It keeps things in place.

45. Pawl Spring

This spring is part of the pawl assembly in the forward assist. It helps create the tension.

46. Pawl Detent

This detent is part of the pawl assembly in the forward assist. It is used in conjunction with the spring.

47. Forward Assist Pawl

The pal is a spring loaded part that is meant to grip the teeth located on the side of the BCG. To allow you to force the bolt into place if it is not working properly. Note: if it is not working properly, do not force it and use it anyway, unless it is a life and death situation as it could very well cost you your life.

48. Forward Assist Spring Pin

The spring that gives the forward assist assembly the overall tension. It removes the pawl from touching the BCG during normal operation.

49. Upper Receiver

The top half of the receiver of the weapon. The part that attaches the barrel to the lower receiver.

50. Ejection Port Cover Pin

This is the pin that connects the ejection port cover to the upper receiver. It also acts as a pivot for the cover to rotate on when it opens and closes.

51. Ring, Retaining Cover

This little retaining ring is what holds the ejection port cover pin in place.

52. Ejection Port Cover Spring

This spring is what allows for the ejection port cover to be opened very quickly and holds it open so it does not shake, rattle or inadvertently close.

53. Ejection Port Cover

This is the little door that keeps the ejection port clean when closed.

54. Handguard Snap Ring

This snap ring is part of this type of hand guard assembly. It functions to act as a platform for the weld springs to tension against.

55. Weld Spring

A spring assembly that is meant to provide tension for the handguard.

56. Delta Ring

This ring is used in conjunction with specific hand guard assemblies. It is an integral component and often needs replacement when scared or damaged. It keeps the rear of the hand guard centered on the barrel at the upper receiver.

57. Carbine Gas Tube

The gas tube is what carries a bit of the gas released when firing a round, from the gas block to the bolt key on the BCG. It is usually housed underneath the handguard.

58. Barrel Indexing Pin

This small pin on the top of the barrel is used to index and keep it in an upright position during installation and use.

59. Barrel Extension

This is the part of the barrel that recesses into the upper receiver. It typically fits into place snuggly and may need to be installed by a gunsmith with proper copper Aeroshell anti-seize applied.

60. Thermoset Handguard

This handguard is a thermoset 2 piece handguard that has a retro look and feel. It is not a free float type handguard that has become a popular replacement.

61. Handguard Cap

This part caps the handguard and holds the top and bottom halves together.

62. Front Sight Post

This is the part of the front sight that is used to identify the area through the rear aperture of the place the projectile should land.

63. Front Sight Detent

This is used to keep tension on the front sight post and keep it from moving

64. Front Sight Detent Spring

This is the spring that is used to create the tension on the front sight detent.

65. Gas Tube Roll Pin

This hardened steel roll pin is used to keep the gas tube in place.

66. Front Sight Bae with Bayonet Lug

This front sight base acts at the gas block as well as the front sight. This particular model comes with a bayonet lug attachment.

67. Barrel Subassembly

A barrel subassembly is the name for a barrel that contains the barrel indexing pin, holes, rifling, and threading.

68. Front Sight Taper Pins

These pins are the proper way to affix a front sight base to a barrel. They should be machined to the proper taper from high quality steel or stainless steel. They can be coated or uncoated.

69. Barrel Nut

This large nut is used to hold the barrel securely to the upper receiver. It requires proper torquing. Check the manufacturer's specs.

70. Front Sling Swivel Rivet

The ritet used to mount the front sling attachment point to the front sight.

71. Front Sling Swivel

This is the front sling attachment point.

72. Crush Washer

This washer is used to securely hold the muzzle device in place. It is called a crush washer because it is meant to crush and allow for the muzzle device to be adjusted to an upright position. Caution: these washers if over tightened will crack, making them useless.

73. Flash Suppressor

This muzzle device is a flash suppressor it could also be replaced with a flash hider, muzzle break, sound suppressor, etc.

74. Buffer Spring

This spring is the driving force that returns the BCG to its ready position. 

75. Buffer Assembly

This is the weighted portion of the buffer components. It creates the inertia. It can come in different weights for different uses.

76. Pin, Buttstock Slide Lock

This pin is used to keep the buttstock in place in one of the positioned holes in the buffer tube.

77. Lock Pin Spring

This spring holds the pin lock into place until the lever is deployed to move and adjust the location of the buttstock.

78. Telescoping Buttstock

This polymer buttstock is a mil-spec telescoping stock.

79. Telescoping Latch

This is the latch that allows, when depressed, the buttstock to be adjusted forward or back and locked into place into any of the 6 position machined into the buffer tube.

80. Lockpin Nut

The lockpin nut keeps the telescoping latch in place.

81. Roll Pin

This little roll pin holds the Lockpin nut into place.

82. Buffer Tube, 6 Position Receiver Extension

This houses the buffer spring and buffer assembly. It can be mil-spec as this one is, or commercial grade that has a slightly different diameter.

83. Receiver Extension Nut

This nut hold the receiver extension, buffer tube, in place.

84. Collar, Buttstock Tube Lock

This hold the the buffer tube securely and does not allow it to spin or turn.

85. Hammer with J Pin

This hammer is the part that strikes the firing pin when the trigger is squeezed.

86. Buffer Retainer

The small buffer retainer detent style part.

87. Buffer Retainer Spring

This spring applies tension to the buffer retainer.

88. Lower Receiver

This is the portion of the weapon that houses the trigger and the magazine that holds the ammunition. Note: this is the only part of the entire weapon that you must register and purchase from a dealer who holds an FFL.

89. Takedown Pin Spring

This spring deploys the tension to the detent that holds the takedown pin in place.

90. Takedown Pin Detent

This is the detent that with the help of the takedown pin spring, keeps the takedown pin on the lower receiver when separating the upper receiver and lower receivers.

91. Rear Takedown Pin

This is one of two pins that are used to hold the upper and lower receivers together.

92. Safety Detent

The small detent used with the safety detent spring to maintain tension on the safety switch.

93. Safety Detent Spring

The spring that is used to create pressure on the safety detent.

94. Lock Washer

This lock washer helps keep the Pistol Grip Screw in place.

95. Pistol Grip Screw

This is the method used to hold the pistol grip in place on the lower receiver.

96. Hammer and Trigger Pins

These pins hold the hammer and trigger in place and are creatively designed to prevent the pins from walking out, or vibrating, which can cause damage to your receiver.

97. Hammer Spring

This is the spring that sends the hammer, when released by the trigger, forward to strike the firing pin.

98. Safety Selector

This is the selector or lever, located on the lower receiver, for switching the weapon from a safe position to a ot or live position.

99. Bolt Catch

This is the component used to catch and hold the bolt in the back position as well as the lever used to release it.

100. Bolt Catch Roll Pin

This is the roll pin used to secure the bolt catch to the lower receiver as well as create the pivot pint for the catch and lever.

101. Bolt Catch Plunger

This part with the help of the bolt catch spring create pressure on the bolt catch.

102. Bolt Catch Spring

This is the spring used to create the pressure on the bolt catch.

103. Magazine Catch

This is the part of the weapon that catches and holds the magazine in the lower when inserted.

104. Pivot Pin Spring

This is the tiny spring that presses on the spring detent and secures the pivot pin in place.

105. Pivot Pin Detent

This little detent holds the pivot pin in place with help from the pivot pin spring.

106. Pivot Pin

This is the front pin that holds the upper and lower receivers together. The front pin was designed to allow for the upper receiver and lower receiver to open and allow access to the innards of the weapon with completely removing the upper and lower halves.

107. Magazine Catch Button

This is the button that when depressed releases the magazine from the lower receiver.

108. Magazine Catch Spring

This is the spring that creates the tension that holds the magazine catch in place so it does not accidentally release the magazine.

109. Trigger Guard Pivot Roll Pin

This roll pin is used to hold the rear of the trigger guard in place as well as double as a pivot for the guard if it needs to be swung out of the way for maintenance or cleaning.

110. Trigger Guard Assembly

This part protects the trigger from getting damaged, as well as snagged. It can be made from polymer, metal, or even integrated into the lower receiver itself.

111. Trigger

The trigger is the last part of the weapon that you use to send the projectile forward fast. The trigger is the part that releases the hammer that strikes the firing pin.

112. Disconnector Spring

It is the small spring that is flared at one end. It is meant to be inserted into the trigger so the flared end goes into the rear of the trigger. It is the spring that releases the disconnector.

113. Disconnector

The disconnector has a two purposes in semi-automatic weapons. One of them is to disengage the connection between the trigger and the sear (aka: hammer or striker) each time a shot is fired. This ensures that the trigger must be released to reset or reconnect the trigger to the part from which it was disconnected in order to fire the next shot. This makes sure the weapon is semi-automatic. Note: just removing the disconnector will not safely transform your weapon into a automatic weapon.

114. Trigger Spring

This is the spring that returns the trigger to the "unpulled" forward position and helps create the tension on the trigger when pulled.

115. Pistol Grip

This is the part that you hold onto with the hand that has your trigger finger. It can be made of polymer, wood, or metal.

116. Magazine Box

This is the surround of the magazine. Newer magazines come as unibody polymer that do not have the same components as the metal versions.

117. Magazine Floor Plate

This is the bottom of the magazine, it is the portion that the magazine spring rests against.

118. Magazine Follower

This is the part of the magazine that the ammunition rest against that presses the remaining rounds into place at the top of the magazine.

119. Magazine Spring

This is the spring that creates the tension that holds the ready rounds at the top of the magazine.