Marvel Adjustable Sight Conversion Unit, 3 mags with extended base pads, barrel is threaded 1/2x28 for .22 suppressor. Includes knurled thread protector. Unit works great with or without suppressor and is extremely accurate. Excellent condition. I paid $440 new from Marvel ($355 for unit + $85 in extra mags/base pads) plus $80 to have the threading done. Price is $300 shipped.