AR-15 lower parts kits and related components. A lower parts kit (LPK) contains everything below the upper receiver except the trigger group, stock, pistol grip, and lower receiver itself — fire control parts, springs, detents, takedown pins, bolt catch, magazine catch, and safety selector. Required for every AR-15 build.
What an LPK includes
- Fire control parts — hammer, trigger, disconnector, and their springs. Standard kits ship with mil-spec single-stage fire control. Upgrade to a drop-in trigger separately if you want a lighter or two-stage pull.
- Pins and detents — front and rear takedown pins, pivot pin detent, takedown pin detent, hammer and trigger pins, safety detent, buffer retainer pin and spring.
- Bolt catch and magazine catch — bolt catch, bolt catch plunger, bolt catch roll pin, magazine catch button, magazine catch spring, magazine release.
- Safety selector — safety lever, safety detent, safety detent spring. Some enhanced kits include an ambi safety selector instead.
Standard vs enhanced kits
Standard mil-spec LPKs (like the Spike's Tactical kit) use stamped-steel parts and are the right call for a budget build or a beater rifle. Enhanced kits (like Strike Industries Enhanced LPK) substitute machined or upgraded parts for the bolt catch, magazine release, and takedown pins — worth the extra spend if you want anti-walk pins or improved ergonomics.
Where the LPK fits in the build
The LPK is one of the last items you install on a stripped lower. See our sub-$400 AR-15 build list for a parts breakdown that puts the LPK in context, and our AR-15 accessories guide for upgrade priorities after the rifle is functional. Pair the LPK with a handguard sized to your barrel and gas system.
State laws on lower receivers and certain configurations vary. Verify local regulations before purchasing or building.
