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This guide is is created to help put together an AR-15 lower receiver from a stripped receiver and a lower receiver parts kit. Please send any questions, suggestions, corrections, and helpful tips to webmaster@ar15.com.

Tools

There are a few tools that make it easier to put together these kits, but none of them are necessary. Minimum requirements include a hammer and punch to drive in a couple of roll pins, a flat-blade screwdriver for A2 stock screw, and either a screwdriver or Allen key for the pistol grip screw. Specialized tools are available from Brownells, at 515-623-4000.

Roll Pin Punches - to drive roll pins (3/32", 1/8", 5/32"); these have a small raised projection in the face of the punch to automatically center the punch and prevent the roll pin from collapsing
Roll Pin Holders - used to hold and start roll pins... very convenient
Hammer - used to drive the roll pins
#10 Flat-Blade Screwdriver - used for A2 stock screw and some pistol grips
Block of wood - base to support receiver when driving roll pins
Pivot Pin Installation Tool - handy tool if you build a few lowers
Allen Key - used for some pistol grips
Telescoping Stock Wrench - to tighten telescoping stock lock ring

The Parts

The lower receiver parts kit consists of 30 parts not counting the stock assembly, the receiver, or the pistol grip. It is a good idea to lay all your parts out on a flat, light-colored surface so that you can verify all your parts are there, and find them easily when you need them.

Most parts kits come covered in oil to prevent rust; wipe all the excess oil off before assembly. Because of tight tolerances, some of these parts will be a tight fit. With the exception of the roll pins, no part should need to be hammered into place.

SPRINGS

Bolt Catch Spring - easily confused with the disconnector spring; disconnector spring is tapered though.
Buffer Retainer Spring - second largest spring in the kit.
Disconnector Spring - similar to bolt-catch spring, but identifiable because one end is wide than the other.
Hammer Spring - larger of the two similar springs.
Magazine Catch Spring - this is the largest spring in the kit.
Pivot Detent Spring - same as the takedown detent spring, so there are two in a kit.
Selector Spring - similar to the takedown and pivot detent springs, but there will only be one of these.
Takedown Detent Spring - same as the pivot detent spring, so there are two in a kit.
Trigger Spring - the smaller of the two similar springs.

PINS
Bolt Catch Buffer
Bolt Catch Roll Pin - smaller of the two roll pins.
Hammer Pin - same as trigger pin; can be inserted from either side.
Pivot Detent - same as takedown detent; both sides usually rounded.
Pivot Pin - larger of the two large pins.
Selector Detent - one end is flat, the other pointed.
Takedown Detent - same as pivot detent; both sides usually rounded.

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