Hi Kody, Yes it includes a 3.5" threaded stainless steel barrel with barrel cap and adapter.

yes the adapter is included see********The Ruger SR22 is a double action/single action semi automatic pistol with a lightweight polymer frame, aluminum slide and replaceable stainless steel barrel. The barrel is threaded with standard 1/2x28 threads for use with a suppressor (not included). Accurate, easy to operate and fun to shoot, the SR22 is a great choice for target, plinking, small game hunting and pest control.
Specifications and Features
Ruger 3604
.22 Long Rifle
Double action/single action semi automatic
3.5" threaded stainless steel barrel with barrel cap and *******adapter
10 rounds capacity
Polymer frame
Aluminum slide
3-dot sights
Two interchangeable rubberized grips
Accessory rail
Overall length 6.4"
Height 4.9"
Weight 17.5 oz
Black

Kody, yes it is included. Comes with a 3.5" threaded stainless steel barrel with barrel cap and adapter.