AT3™ MOTHERFU-BAG™ – The BIG AR-15 Lost Parts Kit – Springs, Detents, Wear Parts, and More


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AT3™ Mil-Spec AR-15 Firing Pin

AT3™ Mil-Spec AR-15 Firing Pin


Launch a detent?  Snap a spring?  Don’t get mad, just fix it with this AR-15 Lost Parts Kit!

Alright, so y’all seem to like the FU-BAG.  Like a lot.  Which probably means there’s a lot of little springs, detents, and pins lying around in dark corners around America.  But we’ve heard you asking for more.  More ways to get you out of that hole after you’ve  F***ed Up – Building A Gun.

Here’s our answer.  To better fit the rage we’ve all felt as springs bend, cotter pins break, or when guns just plain stop working right, we’ve come up with a new kit for all those lost and wear parts your gun needs.  The MOTHERFU-Bag contains a big mix of upper and lower parts for the AR-15 that commonly get lost, break, wear out, or just plain bend too far out of whack to use again.

As always, remember to wear your eye protection whenever you’re dealing with parts under spring tension.  Trying to fix an AR with no depth perception isn’t the easiest thing in the world.

American Made Quality

  • All parts meet or exceed military specifications (Mil-Spec)
  • Components are 100% Made in the USA
  • Backed by the AT3 Lifetime Warranty

The MOTHERFU-BAG Includes:

  • Hammer Spring
  • Trigger Spring
  • Disconnector Spring
  • (2) Hammer/Trigger Pin
  • (2) Firing Pin Retainer
  • (3) Gas Ring
  • Extractor O-Ring
  • Extractor Spring
  • Bolt catch plunger
  • Bolt catch roll pin
  • Bolt catch spring
  • Buffer retainer
  • Buffer retainer spring
  • Magazine catch spring
  • Selector detent
  • Selector detent spring
  • (2) Takedown/Pivot pin detent
  • (2) Takedown/Pivot pin detent spring
  • Trigger guard roll pin
  • (2) Gas Tube Roll Pins
  • (1) Adhesive bandage for any other boo-boos you make


QuantitySingle, 3-Pack

Have Questions About this Product?

The AT3 Tactical store has a 90 day no-hassle return policy for products in good condition. You can view the full details of our return policy here.

If you encounter an issue or defect with a product after 90 days of your purchase, you can refer to the manufacturer for a warranty claim. Their policies are below.

AT3 Lifetime Warranty Logo

All AT3 Tactical Brand Products carry a lifetime warranty against manufacturer’s defects.

This includes AT3 Red Dot SightsHandguardsIron Sights, and any other product that carries the “AT3 Tactical” or “AT3™” name. For other brands (ex. Magpul or Troy), please refer to the manufacturer’s warranty policy.

In the event that your AT3™ product becomes unusable, we will repair or replace the product at no charge to you.

If we cannot repair your product, we will replace it with a product in perfect working order of equal or better physical condition. The warranty is fully transferable, but we may require information about the original purchase to validate the authenticity of the product.

If your product is in need of warranty service, please contact AT3 Tactical to start the process

Our contact info is available here. To expedite processing, please provide your order information and description of the defect.

Please note: The AT3 Lifetime Warranty does not cover loss, theft, intentional damage or cosmetic damage that doesn’t affect the performance of the product.

Customer Reviews

Based on 27 reviews
Happy With The Purchase

The AT3 Motherfu-Bag is exactly what I need on hand if I should have an issue with mt AR-15. It was recommended to me by my firearm instructor...Great product. I also want to comment on the great customer service and fast shipping. AT3 is my go-to-place for AR-15 products.

Delfino Velasco
Handy to Have

Took my AR to paint and sure enough lost, bent, and broke some little parts. Well everything I needed was in bag. Also went ahead replaced the gas rings and trigger springs. Now need to reorder another bag just have in range bag.

Thank you for your feedback! We're glad to know that the AT3 Motherfu-Bag has been helpful in your quest to keep your AR running smoothly. Keep an eye out for our next sale - we've got a discount code just for our readers!

Daniel Gallagher
At3 does it all.

I love this product . Knowing that I have all the kibbles and bits in my pack incase I loose or break something is outstanding fie a reformed Fudd like myself.

Great review! This kit is perfect for anyone who loves to shoot, and wants to be prepared for any mishaps. I definitely recommend it.

Tim McArthur
Must have!

A must need for all AR owners!

Thanks for the feedback! We agree, this kit is a must have for all AR owners.

William Strickland
Saved me more times than I can count

I love to build and tinker with ARs. I am not a very organized person though. My work area is barely controlled chaos but it gets the job done. I can’t count the times that a spring or detent has gone flying into the black hole behind my workbench. I’ve also dealt with bent or faulty roll pins due to poor quality in some rifles. I always keep one of these kits though and can deal with pretty much any situation. I’ve also used it to replace worn out gas rings and they work great. I’m going to buy another 2 right now.

Thanks for the review! This is a great tool for anyone with an AR build. It has saved me a lot of time and money in the past.