Taking off Sr15 Castle Nut

What wrench should I use to take off the sr15 castle nut on my mod 2? I know there's a $60 wrench from brownells, but it's been out of stock for a while. Should I just use some pliers and replace it with an FCD nut? I'm wanting to put a law folder on it.


If you mean the receiver extension castle nut (I try not to assume) there are flat bar wrenches for that and a few other functions for like $10.
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Even spanner style single hooks for more like $3-4
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The multi-function wrenches are mostly more like $25 and readily available everywhere. Just search for AR15 wrench on google, amazon, or your favorite online gun shops. They should be around.

LOTS of variations and specialty wrenches as well.