AR-15 Lower Parts Kit
The A-Z of AR-15 Lower Parts Kit Terms
80% Lower Receiver – a lower receiver unit with 20% of the milling process unfinished. Milling out and drilling the compartment for the fire control group and selector switch and drilling holes for the hammer and trigger pins would be required prior to installation of a lower parts kit.
95% Lower Receiver – an 80% lower receiver with the pocket in front of the buffer tube pre-drilled.
AR-15 Combination Wrench – an AR-15 specific tool used to install the buffer assembly and when working with the barrel, flash suppressors or compensators.
Billet Lower Receiver – a lower receiver cut from aluminum that has been rolled and compressed into a solid block.
Bolt Catch Group – comprised of the bolt catch, bolt catch plunger, bolt catch spring and bolt catch roll pin. This group stops the bolt from moving forward when the magazine is empty.
Buffer Extension Tube – helps to absorb recoil when firing and pushes the bolt back into a forward position, allowing the weapon to cycle and seat another round.
Buffer/Lower Receiver Extension and Stock Attachment Group – consists of the takedown pin, takedown pin detent spring, takedown pin detent, buffer extension, buffer, buffer spring, retainer, retainer spring and stock. For telescoping stocks, a backplate and castle nut are also needed.
Bullet Button – replaces the magazine catch button in a California Compliant lower parts kit. When this button is maneuvered with the tip of a bullet, the magazine will release.
California Compliant Lower Parts Kit – a kit in which the magazine catch button is replaced with a bullet button or magazine locking device.
Cast Lower Receiver – a lower receiver initially formed by pouring molten aluminum into a mold.
Complete Lower Receiver - operates as a firearm once it is attached to an upper receiver. The machining process is finished, and the fire control group, magazine release, grip, buffer tube, buffer spring and stock have already been assembled prior to purchase.
Drift Pins – tools used to align holes for fastening.
Dry-Fire – a fire control group function test by pulling the trigger without having ammunition loaded.
Enhanced Lower Parts Kit – a lower parts kit which consists of at least one alternate part option than a standard lower parts kit.
Fire Control Group – comprised of the trigger assembly and hammer assembly. This group causes the rifle to fire when the trigger is pulled.
Fixed Stock – maintains only one position and cannot be extended or compacted.
Forged Lower Receiver – a lower receiver initially shaped by hammering aluminum into dies.
Gunsmithing Screwdriver Set – instead of tapering at the end like standard screwdrivers, these tools allow the blade to completely fill the slot of the screw. This design provides more torque and decreases the chances of slipping or disfiguring the screw head.
Hammer Assembly – comprised of the hammer, hammer spring and hammer pin.
Hammer Block – a device which protects the lower receiver frame from the hammer movement during function testing.
Handgrip – provides a convenient place to hold the AR-15 while firing and to help manage recoil.
Handgrip and Selector Switch Group – consists of the safety selector, selector detent, selector detent spring, pistol grip, pistol grip lock washer and pistol grip screw.
Lower Parts Kit – the parts needed to install the internal operating mechanisms in the lower receiver including: the trigger guard group; magazine catch group, bolt catch, fire control group, selector switch and handgrip groups, buffer/lower receiver extension and stock attachment group, and the pivot pin and takedown pin group. Standard kits tend to consist of approximately thirty pieces.
Lower Receiver – the portion of the rifle that acts as a housing unit for the firearm’s operative parts .
Magazine Catch Group – comprised of the magazine catch, magazine catch button and magazine catch spring. The magazine is held in place and released by these parts.
Mil-Spec – mandatory standards and technical requirements developed by the United States government’s General Accountability Office. They pertain to equipment utilized by the military, partially with the intention of ensuring operability while also allowing for compatibility and interchangeability.
Mil-Spec Lower Parts Kit – lower receiver parts which, at best, have been constructed identically to those utilized for military rifles. Lower parts kits for consumers are not truly mil-spec due to the fact they have not been inspected and tested by the government.
Pivot Pin - acts as a hinge, allowing access to the inner workings of the upper and lower receivers.
Pivot Pin Installation Tool – an AR-15 specific tool used to hold the detent and spring in place during installation of the pivot pin.
Punch Set – tools used to drive tiny objects, such as roll pins.
Selector Switch – allows the user to choose between “safe” and “fire” modes.
Selector Switchand Handgrip Group – consists of the safety selector, selector detent, selector detent spring, pistol grip, pistol grip lock washer and pistol grip screw.
Stock Attachment and Buffer/Lower Receiver Extension Group – consists of the takedown pin, takedown pin detent spring, takedown pin detent, buffer extension, buffer, buffer spring, retainer, retainer spring and stock. For telescoping stocks, a backplate and castle nut are also needed.
Stripped Lower Receiver – a lower receiver unit devoid of the operative parts/lower parts kit that would make it a complete lower receiver.
Takedown Pin – holds the upper and lower receiver together.
Telescoping Stock –can be extended or compacted due to its ability to fold into itself.
Trigger Assembly – comprised of the trigger, trigger pin, trigger spring, disconnector and disconnector spring.
Trigger Guard Group – comprised of the trigger guard and the trigger guard roll pin. The purpose of the trigger guard is to surround and protect the trigger to avoid unintentional discharge of the firearm.
Trigger Guard Installation Fixture – a holding device which helps to protect the trigger guard flanges on the lower receiver from breaking during installation.