Use this spacer to set the distance for AR15 rifles in 22LR caliber and using a normal rimfire silencer. The thread difference between the two requires this spacer for proper operation. Most AR15 rifles are threaded .600″ length of threads and a proper rimfire thread length is .400″ so this spacer accounts for that difference and makes the rimfire silencer fit correctly when using 22LR uppers on your carbine.

Note: measure the length of your threads, if they are already .400″ or close to that, you don’t need this adapter.