Most AR15s come with a modular handguard, which will offer picatinny, M-LOK, or KeyMod accessory attachment slots. These slots allow you to attach iron sights, lights, lasers, foregrips, bipods, slings, bayonets, and any other necessary additions. Depending on the handguard, your attachment system will vary, so it is important to understand the differences between the three most popular options. Picatinny rails (Pic rails) are the old-school way to mount everything to your gun. These days, most rifles will have a pic rail on top for optic and sight mounting. M-LOK and KeyMod are the 2 newer standards for all other accessories and have been in direct competition. They both offer their own benefits, but M-LOK is the more popular option, offering a greater variety of compatible parts and accessories. If you are buying your first AR 15 and are uncertain about handguards, we highly recommend that you look at rifles with M-LOK handguards, as you’ll always be able to find compatible parts.