Field repair kit
Field repair lower parts kit for the AR-15 rifle.
Misc common items
Miscelaneous small repair and replacement items 
Here we have the various small parts and replacement parts for the AR-15 and M-16 Lower receivers.  You can find most of the little things that may come up missing or need to be replaced without having to purchase a complete lower parts kit.
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Field repair kit
AR785
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AR-15 field repair kit.

Includes all of the parts most likely to break, wear out, or be lost. Includes: firing pin, 2 firing pin retainers, bolt cam pin, 3 bolt gas rings, buffer detent, buffer detent spring, extractor, extractor pin, 2 extractor springs & pads, disconnector spring, disconnector, hammer spring, and trigger spring.

OOPS Replacement Kit
AR791
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lost it kit
AR15 small item replacement parts kit. 
OOPS! Replacement Kit.

Includes replacements of the most commonly lost or damaged accidently parts.  Includes 4 takedown pin detents, 4 takedown pin detent springs, 2 buffer detents, 2 buffer detent springs, 2 firing pin retainers, 2 selector detents,2 selector detent springs, and 2 extractor springs and pads.