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Mil-spec buffer tubes, springs, buffers, and castle nuts for every AR rifle and pistol.

Most lower parts kits do not come with a buffer tube. That's because slight variances in receiver buffer tube housing dimensions mean that the threads on one tube may not work with a particular receiver. That's determined by whether your receiver is "commercial" or "mil-spec." We sell exclusively mil-spec buffer tubes since most receivers fit this measurement.

Not sure which tube you need? Read our guide comparing mil-spec and commercial tubes.

What's in a Buffer Tube Kit?

Our buffer tube kits include all the other stuff your lower parts kit doesn't come with, so you can complete the assembly of your fabricated 80% lower or retail-bought stripped AR lower receiver. Each buffer tube kit includes the following components:

  • Threaded buffer tube with stock/brace position latch holes
  • AR-15 (3.0-oz) or LR-308/AR-10 "Shorty" (5.4-oz) buffer
  • Mil-spec threaded castle nut and notched latch plate
  • Mil-spec, universal AR recoil spring

Not sure which buffer you need? Read the guide to AR buffers and weights.

LPK-and-Buffer-Tube Combo Kits Available

Want everything required to assemble your lower? Take out the guess work and grab an AR-15 or LR-308 lower build kit. Each kit comes with a full buffer tube kit for your 5.56/.223 or .308 build, as well as a mil-spec stock and full lower parts kit with hammer, trigger, safety, disconnector, and all springs, pins, and detents required for the LPK install. We even have a kit that includes all of the above, plus an AR-15 80% lower! All you'll need is an upper assembly, a little time to fabricate your lower, and you're ready to hit the range.

Tools Required for Assembly

If you've got your lower parts kit and buffer tube ready for assembly, you'll need a few specialty hand tools to get the job done:

Use our guide on how to install the lower parts kit! It includes instructions for installing your buffer assembly, too.

DISCLAIMER: If you are new to the world of DIY gun building, you likely have a lot of questions and rightfully so. It’s an area that has a lot of questions that, without the correct answers, could have some serious implications. At, we are by no means providing this content on our website to serve as legal advice or legal counsel. We encourage each and every builder to perform their own research around their respective State laws as well as educating themselves on the Federal laws. When performing your own research, please be sure that you are getting your information from a reliable source.

We are a national retailer of individual components and not all products depicted on this website are legal in every state. Shipping of various products found on this website are prohibited to some states (such as California, Connecticut, District of Columbia, Hawaii, New Jersey, New York, Rhode Island, and Washington). The information, pictures, text or products presented on this website are not a representation by us, and should not be understood by you, that any product or completed firearm is legal to assemble or own in your state of residence. We encourage each and every builder to perform their own research about the state and federal laws that apply to them. It is your responsibility to understand the law and we encourage you to consult with an attorney or your local ATF representative.