Short answer: a lower parts kit (LPK) holds the small parts that turn a stripped lower into a working one: the safety, bolt catch, magazine catch, pins, springs and detents, a trigger guard, and usually a pistol grip. Many kits leave out the fire control group (hammer, trigger and disconnector) so you can add an upgraded trigger: Geissele's Standard and Ultra Duty kits do, while BCM's Enhanced kit includes its PNT trigger. Decide on your trigger first, then buy the kit that matches.
What is in an AR-15 lower parts kit?
| Group | Parts | Geissele Standard (with grip) | Geissele Ultra Duty (no grip) | BCM Enhanced |
|---|---|---|---|---|
| Fire control group | Hammer, trigger, disconnector, springs, hammer and trigger pins | Not included | Not included | BCM PNT trigger assembly |
| Controls | Safety selector and detent, bolt catch, magazine catch, button and spring | Posi-Snap safety | Ambidextrous Super Configurable safety, Maritime bolt catch | Mil-spec safety and bolt catch |
| Pins and detents | Takedown and pivot pins, detents and springs, buffer retainer and spring | Included | Included (checkered pins) | Included |
| Trigger guard | Guard and roll pin | Mil-spec trigger guard | Billet 7075-T6 trigger guard | BCM enhanced trigger guard |
| Pistol grip | Grip, screw, washer | A2 grip | Not included | BCM Mod 3 grip |
Contents are from Geissele's Standard and Ultra Duty kit pages and BCM's Enhanced kit page, read October 2026.
With or without the trigger group?
- Without the fire control group: buy this if you are fitting a drop-in or upgraded trigger. See our best AR-15 triggers and trigger comparison.
- With it: one box completes the lower. BCM says its PNT trigger and hammer are investment castings to the USGI technical data package with honed pin holes and a polished, nickel-Teflon finish.
- Without the grip: Geissele sells the Ultra Duty kit with no grip, so you can fit your own; see our best pistol grips.
Mil-spec or enhanced?
A standard kit uses mil-spec parts. Enhanced kits swap some for upgrades: Geissele's Ultra Duty adds an ambidextrous safety, an extended Maritime bolt catch, checkered pins and a billet aluminum trigger guard, and says its key components are stainless steel. If you want controls on both sides, see ambidextrous AR-15 lowers and controls.
Trigger guards
The trigger guard closes the bottom of the trigger well. A mil-spec guard is held by a roll pin. Magpul says its polymer MOE Enhanced guard is enlarged for gloves, fills the gap behind the guard, and fastens with set screws instead of a roll pin; Geissele's Ultra Duty guard is machined from billet aluminum. Some lowers have the guard built in, so check yours before buying one. The roll pin is the trickiest part of most builds: our lower assembly guide shows how to support the ears while you drive it.
Lower parts kits, with today's prices
Lowest price across the stores we track:
BCM Enhanced AR-15 lower parts kit
Pros
- Includes BCM PNT trigger and hammer
- Mod 3 grip and enhanced trigger guard
Cons
- Single-side safety
Complete kit
Geissele Standard lower parts kit with grip
Pros
- Posi-Snap safety, A2 grip
- Room for your own trigger
Cons
- No hammer, trigger or disconnector
For an upgraded trigger
Geissele Ultra Duty lower parts kit
Pros
- Ambidextrous safety, Maritime bolt catch
- Billet 7075-T6 trigger guard
Cons
- No trigger group and no grip
Enhanced
Spike's Tactical standard lower parts kit with fire control group
Pros
- Listed with the fire control group and trigger
Cons
- Check the listing for the grip
Standard with trigger
LBE Unlimited lower parts kit with trigger guard and grip
Pros
- Listed with trigger guard and pistol grip
Cons
- Check the listing for the trigger group
Budget
Trigger guards, with today's prices
Magpul MOE enhanced trigger guard
Pros
- Enlarged for gloves, fills the gap behind the guard
- Set screws instead of a roll pin
Cons
- Polymer
Enhanced guard
B5 Systems Bravo aluminum trigger guard
Pros
- Aluminum guard
Cons
- Few published specs here
Aluminum
Compare every lower part and trigger by price, and plan your build in the AR-15 builder. Thinking of buying a lower already assembled? See build it yourself or buy.
Frequently asked questions
What comes in an AR-15 lower parts kit?
The safety selector, bolt catch, magazine catch and button, takedown and pivot pins with their detents and springs, buffer retainer, trigger guard and usually a pistol grip. Some kits also include the hammer, trigger and disconnector.
Does a lower parts kit include the trigger?
Not always. Geissele's Standard and Ultra Duty kits leave out the fire control group; BCM's Enhanced kit includes its PNT trigger.
Does a lower parts kit include the buffer tube?
No. It has the buffer retainer and spring, but the tube, buffer, spring and stock come separately or in a stock kit.
What is the best AR-15 lower parts kit?
BCM's Enhanced kit if you want one box with a trigger; Geissele's Standard if you are fitting your own trigger; Geissele's Ultra Duty for an ambidextrous safety and billet trigger guard.
What does a trigger guard do on an AR-15?
It shields the trigger. A mil-spec guard is held by a roll pin; Magpul's polymer MOE guard uses set screws and is enlarged for gloves.
Are lower parts kits universal?
Mil-spec kits fit mil-spec AR-15 lowers. AR-10 lowers need AR-10 parts for some items, and some lowers have built-in trigger guards or ambidextrous controls; check your lower.
